Low compression

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AustHaflinger
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Low compression

Post by AustHaflinger »

As I indicated in this thread http://thehaflinger.com/viewtopic.php?f ... 6&start=20

I have low compression on No2 cylinder.
garrycol wrote:So with the tappets adjusted, power should be back so I decided to do a compression test - last November both cylinders were just over 150psi. This time No 1 cylinder was at 150psi but No 2 cylinder is at 60psi - the engine will run fine on No1 cylinder by itself but will not run on No2 cylinder by itself. So that is the reason I have low power - only one cylinder operating. Spark is all fine.

I ran the engine without the rocker covers on and got exhaust gas out the push rod hole so my guess is there is a broken ring/s in number No cylinder or something like that - or less likely a burnt valve. Blow by also seemed to be pushing exhaust gas and oil out the breather pipe as well.

In theory If I pull the tinwork off I should be able to remove the head and barrel with the engine in place but I am not sure - yes the engine is only held in with 4 bolts but it is all the other stuff that has to be removed that is the pain.

If the engine does have to come out then so does the gearbox as it needs its input shaft bearings done.

So Haffie now gets retired for a year or so so other projects can proceed.

Garry
garrycol wrote:
kerry460 wrote:personally i would not even bother to try it in place
kerry
Yes - but if I go to the extra effort of taking the engine out, then the gearbox has to come out and then I will have to find someone to rebuild it.
Ok - got the the inlet manifold and exhaust off - pushrods out and head bolts off - heads will not come off with the engine is in place as the body work is in the way - it would have been nice if the tappet access hole was larger but it isn't.

Image

Image

Image

So the engine needs to come out - on first look there is nothing obvious yet as to why the compression is low.

More to come

Garry
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heinkeljb
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Re: Low compression

Post by heinkeljb »

Wow, another serious oversight on the part of the designers! Maybe the other side will come off as the cylinders are slightly off set from one another aren't they.

Yes i know taking the engine out is an option, but considering all the ancillaries you have to take off, undo / move it would have been nice just to slide the heads / barrels out of the "not" convenient holes.

Does it look like there is any scoring on the barrel?

I take it the oil that is showing it the oil you used for the compression test? If not, then maybe you have a valve guide failure? If that was the case, I would have thought you would have seen blue smoke when running.

How about posting a video of the engine removal - examination?

John
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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

John - too late for a vid of the removal process as it is now out - who ever said it was a 40min job must have been high on something - wow to go about 6 hours - electrics, manifolds, muffler, tinwork, rear lower X member, brackets - it all adds up with a lot underneath.

So it is out - head looks OK but there is a casting imperfection which I cannot remember if it was there before - maybe errosion. Anyone in the know got an idea?

Image

Image

The top of the piston is OK - the bore is OK but does have a surface mark (not a score) about 1cm wide - maybe where a piece of ring is broken and allow gases past the piston and this is a carbon mark bit definitely no scoring.

I cannot check the rings as I cannot get the barrel out of the crankcase. So how do you do this without breaking the fins???

Admittedly this is a VW barrel but the Haflinger one is exactly the same - why to the makers not have a solid section on each side of the barrel that can be tapped using a small hammer and soft metal drift so that fins are not damaged. I have two spare new barrels and piston assemblies but would prefer not to use them.
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kerry460
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Re: Low compression

Post by kerry460 »

Gary , i was not high on something ,
i said to remove the motor from the vehicle . not to also strip the motor .
i did also state it was the best time ever ,
i did not state YOU should be able to do it .
the only thing removed from the motor before removal from vehicle was the dynastart

i also stated that i had a flange coupling on the exhaust . and a genuine towbar with QD pins .

standard barrels slide in and out with no force , just hands , so i presume whoever did the machining made them too tight .
not S D P,s fault .

kerry
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Re: Low compression

Post by Bigdougal »

It is probably a close run thing between whether it is quicker to take platform off or quicker to drop engine.
Cheers

Doug Hart

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heinkeljb
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Re: Low compression

Post by heinkeljb »

Gary,

Have you tried a hot air gun on the crank cases, Being alloy, they should heat and expand quicker than the barrels. You could make up a tool to help remove the barrels, a "U" piece of metal sheet just thick enough to slide between two fins and long enough to protrude on either side. Would give you something to push against - put two / three lengths of studding through holes and a nut on each. Push against suitably protected crankcase.

The marks on the cylinder head are like those left by a bit of metal flying around in there - except they are confined to one spot - weird - have you had a look at the bottom of the valve guides?

John
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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

kerry460 wrote:Gary , i was not high on something ,

standard barrels slide in and out with no force , just hands , so i presume whoever did the machining made them too tight .
not S D P,s fault .

kerry
Hi Kerry - could only remember the time to pull the engine not who said it - was just kidding :D

I agree the barrels should just slide in an out - not sure but there does seem to be some sort of non drying sealant residue there so may have been sealed - but then could just be oil and dirt. Yes not a SDP issue but I am sure after some issues the SDP barrels could be hard to get out.

As suggested by John I need to think about this a bit more - maybe a little light heat, tools to remove etc - I have three other barrels but would prefer not to use them.

The marks do not look like mechanical damage but more like erosion caused maybe by flame pattern - dunno.

I haven't done any further at this stage. The engine is on the floor with oil still in it as I had anticipated a quick inspection, replace what was needed and reassemble. I will put the engine on the engine stand, drain the oil and then turn the engine to the best position to get the barrel off.

Cheers

Garry
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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

The barrel is held in with no hardening gasket goo.

Taking John's suggestion I applied a bit of propane heat around the base of the barrel and I noticed the gasket was returning to liquid. I gently tapped around the barrel with a rubber mallet and noticed that it started to move - so with gentle tapping, pulling by hand and the gentle application of heat the barrel came out.

Nothing abnormal to the bore - cross hatching still there, not major marks.

Looking at the piston and rings, again nothing obvious no cracks in the rings and they seem in good condition - the something caught my eye. Cracks in the piston between the rings.

Image

There is a crack in the piston metal between the top ring and the second ring and while the metal has been removed in the pic there were three cracks in the piston metal between the the second ring and the oil control ring at the bottom.

The top section is cracked as shown and extends about 2" under the the metal towards the top of the pic. You can see the crack extending just to the side up near where the gudgeon is in the groove for the second ring.

The section between the second ring and the oil control that is missing in the pic was still there and had not fallen out - three crack one at either end and one about 2/3 the length - like the other damage there is a crack under the metal up towards to top of the pic about 1.5" to 2". If I pulled on both top sections above the cracks the metal will pull out.

Interestingly this damage is not in the area where the piston was modified (piston crown) so is not related to modifications. While there are cracks no metal fell out - the low compression was caused as the cracks go into the oil access holes in the piston so some exhaust gases were able to make there way through the inside of the piston to the crankcase.

Any ideas - the piston has only been in about 1200km and the engine has spent most of its life below 4000rpm and has not been over redline. What would cause the rings to remain OK but the piston material between the rings

Cheers

Garry
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Re: Low compression

Post by kerry460 »

wrong rings on piston , ie; rings too tight in ring lads .

piston dropped or damaged before assembly .

faulty casting in piston .

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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

Thanks Kerry - while the wrong rings is always a possibility it would have happened at the Mahle factory as the barrels, pistons and rings come as a kit - so no mix an matching during fitment.

My guess is just a manufacturing fault - but this has me wondering if I will have the same issue later with the other cylinder and with the piston and barrel I will replace the broken on with - all out of the same kit.

These are Mahle brand so not a cheap chinese knockoff.

Before putting the new rings on the new piston I have to do some more research on how they go as the the top ring has a bevelled inner edge and the middle ring has a bevelled outer edge and not sure if the bevelled edges go to the top or bottom.

Cheers

Garry
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Re: Low compression

Post by kerry460 »

ok , bevelled rings ?? i know the answer , but it is hidden in my forgettorr .
i am fairly certain that the top goes bevel up to increase the sealing with pressur .

but do your home work

its late and i am buggered ,
kerry
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Re: Low compression

Post by HaffyHunter »

Hi Garry,

Only two things that I know of will cause the piston damage that you've shown us. Either or a combination of both these are appropriate as you say these are Mahle pistons and so they are forged type.

1) The bore clearance is too tight. Forged pistons require greater bore relief as they expand when heated much more than cast pistons. They also require that the engine be allowed to warm up to normal operating temperature before driving and applying load. This is a common error that many high performance engines encounter when in the hands of those not experienced with running forged pistons.

2) The ring gap is too tight. As I mentioned in an earlier post, the ring gap must be custom set for each application. This is especially true when using forged pistons. There is no way that Mahle can know the exact bore diameter of your engine when they ship the pistons and so leave the rings "raw" for the builder to finish during assembly. In your case it appears that the ring gaps may have been tight and the ring expanded enough to apply excess force to the piston's ring flanges. This would be amplified if the bore clearance was too tight to allow for sufficient piston expansion.

Cheers,
Steve
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Re: Low compression

Post by AustHaflinger »

HaffyHunter wrote:Hi Garry,

Only two things that I know of will cause the piston damage that you've shown us. Either or a combination of both these are appropriate as you say these are Mahle pistons and so they are forged type.

1) The bore clearance is too tight.

2) The ring gap is too tight. As I mentioned in an earlier post, the ring gap must be custom set for each application. This is especially true when using forged pistons. There is no way that Mahle can know the exact bore diameter of your engine when they ship the pistons and so leave the rings "raw" for the builder to finish during assembly.

Cheers,
Steve
Thanks Steve - my pistons are cast pistons - it is only the race pistons that Mahle make that are forged. Also what I have is not a mix and match of barrels, pistons and rings from different sources but a Mahle kit that has everything already in it so barrels, pistons and rings already match - not sourced from this seller but this is the kit I have http://www.mooreparts.com/2956-MAHLEC87/ When the rebuild was done last year I had to get four sets as the kit only comes with four. Hence I have two new spares and the undamaged used barrel and piston from the old engine.

However I do suspect that one of the scenarios you mentioned has happened because the engine has got too hot on one of our very hot days last month. I think the engine has overheated but not enough to seize it as there is no evidence of that but has got very hot causing tolerances to tighten up around the rings - maybe after the rebuild it has not yet fully run in so naturally temps are higher and on a 40c day driving up hills was too much for it.

I think that oil temp gauge might be a priority when it gets back on the road. I am not sure where to plumb it in though.

Cheers

Garry
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Re: Low compression

Post by walderse »

Garry,
Have you considered using this unfortunate situation as an opportunity to return the motor back towards functioning within its original design parameters? Original displacement pistons/rings/cylinders are available. The apparent extremely short lifespan of the originally VW-intended parts does not inspire much confidence in using the remaining pair from that four cylinder kit as replacements.

I do not believe the SDP engineers ever considered pushing the displacement of the original engine block/crankshaft up to the level achieved using an 87mm bore instead of the original 80mm choice. We do know they increased power with the addition of a supercharger to achieve with world record for highest motor vehicle altitude during the 1961 Atacama Expedition and they also designed an in-house four cylinder boxer engine.

Best wishing on getting your motor fully operational as soon as possible.
Take care.
Jim
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Re: Low compression

Post by heinkeljb »

Bad luck Gary!

Send them back to Mahle and ask them what happened....

I assume ( I know not good...), that in order to have fitted the VW barrels the crank cases would have been machined to open them up - going back to standard barrels would be a bit of a problem. You would either have to alter the crank cases again, presumable by Ali welding back in material and then re-machining the holes to standard size. Have a ring / sleeve made up that would fit between standard barrels and the currently altered crank cases.

I know Gary is looking at another engine, but that still leaves an engine which needs to be built correctly. If it is down to wrong clearances on the rings, that must be due to the Haflinger engine running at a different temperature from a VW one.

Alf Polkington here in the UK builds big bore Haflinger engines and has had one in his 6 wheeler for a long time, I wonder why that hasn't gone bang if it is down temperatures? I know he has put in a plate where the original oil cooler fits and has run two pipes out to in front of the firewall to an external oil cooler, but he said that was because the original oil cooler gets in the way of the cooling air- That would be the left hand cylinder and not the right hand one like on Gary's, that would suffer from overheating.

I know Alf is not good with computers, so he would never see this thread to be able to comment.

John
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Re: Low compression

Post by Goatwerks »

A few suggestions: with feeler gauges, measure ring end gaps in bores top ring .005" per 1" bore, 2nd ring .0035" per 1" bore, Oil rings, min gap in bore is .020".
You do not file oil rings.
Going back to stock is not an option as the case is machined to accept the larger cylinders.

Now onto the cause, it looks rapid heat related (tight ring end gap)as there is no dry scoring(plenty of lube), an exhaust leak at the head or Main jets may be too small for the larger bore volumes at higher rpm's. Do you know your jet sizes?
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Re: Low compression

Post by HaffyHunter »

Hi Garry,

As Jim LaGuardia has stated, there appears to be no loss of lubrication as a secondary result of excess engine temperature. If this were the case I would expect to see significant scoring & discolouring on the piston skirts.

Regardless of your pistons being cast (as opposed to forged) and having come with barrels as a set from Mahle I still say that the ring gaps and possibly barrel to piston clearance was too tight. Perhaps Mahle did set gaps and clearances correctly at their shops but there could later have been a mismatch of piston and rings with barrel as it is unlikely that any two will be exactly the same and could easily have been mixed up on a bench.

Cheers,
Steve
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Re: Low compression

Post by AustHaflinger »

Thanks for all the input - much appreciated.

Yes I have considered changing the engine back but what I have is what I have got ;) . The first failure was cause by the person who built the engine not getting tolerances right and as a result the piston was hammering the head and ultimately failed. When the new barrels and pistons were put in last year certain changes were made that increased tolerances and with the head off inspection shows this has all worked. I have an original spare engine case, barrels and pistons and with more parts such as heads, crank and cam could make up another engine but will not do so at the moment.

On the basis of what everyone has said it is clear that the standard ring clearances may be OK for normal use but not when the engine gets hot. So I will check them all (cheers Steve). Jim LaGuardia, if you do not file the ends of the rings how to you take them down to size.

On the bevel issue - I assume on the compression ring the bevel goes down but what about the oil scraper ring? Bevel up or down?

Cheers

Garry
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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

Goatwerks wrote:Going back to stock is not an option as the case is machined to accept the larger cylinders.
I measured the bottom of the standard barrel and it is 84.5mm in diameter - the 87mm barrels I use are 89.5mm in diameter. so 5mm extra. If I were to go back I suppose a ring could be inserted and pinned to the crankcase but I would just use another crankcase.
Goatwerks wrote:Now onto the cause, it looks rapid heat related (tight ring end gap)as there is no dry scoring(plenty of lube), an exhaust leak at the head or Main jets may be too small for the larger bore volumes at higher rpm's. Do you know your jet sizes?
Jim if you recall back to Sep 2013 on the Portal Hub forum you advised the following when I was wanting to change back to the Zenith Carb.

"Haflinger version is closest to the Unimog type. Just change out the jets and venturi inserts.
Venturi 22mm, main jet sizes 95/100/105/110/115, idle jet 45, air correction jet 240, idle air jet 80, pump jet 40, starter jet 190, use the Unimog injection tubes(squirters/part#79 in parts book) as the special Haflinger ones are no longer available.
Easy conversion and uses a std Unimog rebuild kit and same pump length as Pinz, use lowest hole for pump rod."

I bought a Unimog carb complete and a used a Haflinger jet block from Technik Haflinger and had the lot professionally joined and rebuilt - if I remember correctly the mains are up around 115 the rest as above (I think I asked the carby builder to take these out to 120 but not sure if this happened).

The car went onto a dyno tune this time last year and I was told all mixtures were correct across the rev range. I still have the Unimog jet block - suppose I could try the Unimog main jets but I would assume they would be way too big (I cannot make out the number on them but it looks like 140.)

Cheers

Garry
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Re: Low compression

Post by Goatwerks »

I would run the ring gaps on the looser side, monitor head temps and then try larger main jets (#120)and compare readings.
Larger bore needs more cooling(fuel is part of the equation)at higher rpm's.
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