Low compression

[AustHaflinger]

Just been watching some Youtube vids about reassembling VW engines and they use silicon sealant to seal the barrels to the crankcase. Also been reading the Haflinger Workshop manual and no mention is made of using any sealant so I assume it is not used.

My engine builder previously used a non hardening gasket goo that made the barrel hard to get off but it did come off.

So do we use sealant or not?

Thanks

Garry

[kerry460]

i never have between barrel and crankcase .
never had a problem .

kerry

[HaffyHunter]

Hi Garry,

Like Kerry said, I have not used sealant between the barrel and crankcase either and have had no problems. I would be concerned that even the thinnest layer would be a hydraulic barrier that would prevent normal expansion of the barrel's flange when hot thus a tight bore at the bottom and a flaring at the top.

Cheers,
Steve

[walderse]

Garry,
Thanks for the measurement differences in the bottoms of the two cylinders. I am aware that the cases would have to be machined open to allow the larger cylinders to mate with the case. Shimming with some sort of spacer ring would seem the least expensive option if you were to use existing modified cases with original cylinders. What is the difference in diameters of the head ends of the barrels? How much material needed to be removed from the original heads to allow the VW cylinders to fit?

Take care.
Jim Molloy
Waldersee Farm
http://www.northwestmogfest.com

[AustHaflinger]

Garry,
What is the difference in diameters of the head ends of the barrels? How much material needed to be removed from the original heads to allow the VW cylinders to fit?

Take care.
Jim Molloy
Waldersee Farm
http://www.northwestmogfest.com

Hi Jim - the diameter of a standard barrel at the head end is 92mm. The VW barrels on the engine when I bought were 94mm across so 1mm taken out inside the head. However when we had the heads off last year one of the heads (the cylinder that failed) had two small cracks in the combustion chamber where the push rod tubes go through the heads so when the current barrels were to go in the heads were left standard in this aspect and the material taken off the top of the barrel - the logic being it was safe to take a bit of the barrel at this point as it is inside the head and reinforced by it. The heads I use now are not the same ones I had on it originally.

So the outside of my current barrels 92mm the same as original barrels.

Garry

[AustHaflinger]

Ok - I took the piston etc over to the my engine builder and as soon as he sighted it he said it was caused by detonation on the side of the combustion chamber overloading the rings etc on that side - no melting just shock loads.

The reason - who knows - too low octane fuel, timing too advanced at revs, engine too hot, mixture at revs too lean??

So when the engine goes back together, static timing will change from 7 degrees BTDC to 5 degrees BDTC and fuel will go up from our 91 Octane to 98 Octane or at a pinch 95 Octane.

When the engine is running timing at 4000rpm will be checked to see if the mechanical advance is advancing too much and the mixture at those revs also checked.

I also need to pull the head and barrel off the other cylinder to ensure nothing similar has started on that piston.

Oh - ring gaps and barrel distortion was checked and all was OK.

There is also a clue to why the engine failed last year and why the tappets keep closing up. The builder has never previously worked on a Haffie engine but has lots of experience on VWs and motorbikes with a similar crankcase, barrel and head arrangement that is held in by four long studs and bolts. He indicated that on many VWs he has worked on that due to the long thin studs there can be a minute twisting movement with the thousands of pulses going on in the engine every minute. This manifests itself where the head twists on the top of the barrel and wears ever so slightly but over a long period of time it can start the erode the softer aluminium of the head - there is evidence of this type of erosion on my heads. He said that on some engines there are tabs that link the barrel directly to the crankcase to stop any twisting movement and the same locking the head to the barrel leaving the head bolts and studs to just hold the lot in.

On the VW engines he builds he just laps the the barrels to the heads with lapping in paste so the two surfaces mate and if there is movement wear is minimal. Maybe there is a high temp grease that can also be used as a lubrication. Maybe a very thin hardened steel head gasket would help here and allow steel on steel movement rather than steel on aluminium.

So maybe on the old engine the head eroded too much that the piston was impacting the head (there is evidence of that) and the hammering over a long period of time resulted in the structural failure of the piston. Who knows.

So I am out now to remove the other cylinder to check it out.

Garry

[heinkeljb]

Gary,

If it is the case that the barrel / head joint is moving and wearing, for it to impact the valves closing up it would be a lot of wear, very fast. Why not take the old heads and the one you currently are using and get your engine builder to measure the depth of the barrel / head joint.
Only issue might be if the head has been skimmed previously. In which case, do the measurement from the rocker box holes as being the constant. If the barrel /head joints have been the cause, you should be able to come up with measurements that confirm it.

Maybe you need to put a brace from the heads to the crank case using say, a longer stud on an inlet manifold and a crankcase to gearbox mounting bolt?

The detonation part could quite easily be down to the distrubutor weights - the pivots could wear so maybe they provide changing advance, or get stuck at a particular angle?

John

[AustHaflinger]

Hi John - the heads have not been skimmed - the top of the barrel actually sits in a .5mm deep circular trench which I assume is to aid sealing.

As the mechanic said he has not worked on these but the pattern looks similar to what he observes on VWs - of course may not be the case. No one has yet come up with a better suggestion (there is no valve recession) - noting that from comments I have read on the net many other Haffie owners have a similar issue - and it was noted by Haflinger agents who sold the cars from new. Maybe something to live with. Note the heads I have on now are different to the ones I had on before and the issue was the same on both.

The dizzy was new last year so shouldn't be an issue and was certainly working within specs this time last year - but is easily chacked with my timing light once the engine is back together.

No 1 Cylinder is now out and the piston is clear of damage and will go back in as is.

Garry

[heinkeljb]

Gary,

You have a real conundrum on your hands! If it was the distributor that was at fault, why hasn't it shown the same detonation in cylinder 1?
As the only issue is in cylinder 2, that would point to an issue that only affects cylinder 2. So things involved might be:-

Spark plug. (Distributor cap / lead / plug cap?)
Inlet manifold.
Inlet valve.
Exhaust valve.
Push rods. (loose ends or wrong length?)
Piston / Rings. (We know the piston failed)
Barrel (Bore diameter changing over the length?)
Conrod? (Twisted / Bent?)

I can't think of anything more that is specifically that one side of the engine that might have any impact on how it runs.

Guess it is a question of having a good look at each and every one of those items.

John

[AustHaflinger]

I agree - who knows - something has to break first and maybe it just happened to be the piston that went.

The engine needs to go back together first and then to check a number of things such as advance at revs etc.

The concern this time was that the engine has always been operating within it original operating range with correct carb, ignition, inlet manifold etc where the previous version was even more modified with far more unknowns.

Garry

[Goatwerks]

Cylinders are sealed at base with Permatex aviation sealant.
I agree with possible impact to head as ring failure seldom causes this degree of damage.
You may have to trim just a little more from the outer diameter of the top.

[AustHaflinger]

Hi Jim - that sealant is what was used and as I know it goes back to liquid with a bit of heat I will use it again.

We are taking a couple of thou off the outer 1/2" of the piston crowns. As an alternative we could have put a small spacer between the barrel and crankcase or put in a "heat gasket" made out of a large diameter piston ring and while either of these may have worked I would be going into an unknown area. Everything about the pistons works (compression is good, valves clear the crown etc) so taking a little off will just further refine the design.

I have a master piston the changes made first then the changes replicated - this means we are never copying the copies.

Oh - next week the main jets are going in to get measured to ensure they are 120s and if not to take them out to 120. Once the engine is back in and working and run in a bit - we will do some high rev (4500rpm) testing of the mixture and what advance the dizzy weights are actually delivering.

Cheers

Garry

[AustHaflinger]

I finally got my pistons back and 1/2mm was taken off the outside of the crowns of the pistons. When putting one of the pistons back on the conrods I managed to send one of the gudgeon circlips across the garage and was lost (suppose it will turn up in 5 years time) so I went down to a nearby engine builder to get another circlip. I took the damaged piston with me to get a second opinion on the cause of the damage and as soon as he saw it he also said detonation - no ifs, no butts.

Taking .5mm off the pistons will lower compression a little and I with the other actions should see things OK when the pistons and barrels go back on.

Garry

[heinkeljb]

Fingers crossed it will work this time without any further drama!

How are you going to deal with the octane rating of the petrol? Additive to 91, use pump 95 or 98 and more additive? The Hafi tank is not very big, so a bottle of additive will cover 2 or 3 fill ups with ease.

John

[Bigdougal]

John,

What have you been putting in your tank and how have you mixed it?

[AustHaflinger]

Given that compression tests have always shown 150psi which gives a rule of thumb compression ratio of about 9:1 our 91 octane should be OK. I did start running the engine when it was built on 98 octane but after it started to settle in I switched back to 91 octane.

My personal view is that either ignition is too advanced at higher revs or the carby is leaning out at high revs however if anything the spark plugs show it is running a little rich.

There is no mixing of fuels - straight from the petrol pump - I do add valve saver but it is probably not needed as the valve seats are hardened.

So I will go to 98 octane fuel (95 in out of the way places), I will set ignition timing to 5 degrees BTDC rather than the specified 7 degrees, and when the engine is run back in, do a high rev dizzy mechanical advance check to endure it is not advancing too far and a mixture check to ensure it is not running lean at higher revs.

Garry

[AustHaflinger]

Pistons, barrels and heads are back on. Next week will be tappets, tinwork and engine back in the vehicle. I torqued the heads to 20 ft/lbs as specified in the book - any updates on this torque setting?

Cheers

Garry

[heinkeljb]

Hi Gary,

I see in the torque table that was posted on the Yahoo group site along time ago and which apparently comes from a Repair Manual, ( I bought what I thought was the same manual, but it doesn't have the torque table in it) that the nuts are torqued to 2.5 MKP which using an online conversion calculator equates to 18.08248 ft / lbs.

So 20 is not huge percentage over and should work fine.

John

[kerry460]

my paper work says 21 foot pounds . with lubricated threads and thrust faces .

earlier you discussed ring gap .
my records are 12 to 18 thou . but that is Haffy components

ask if you want more

kerry

[AustHaflinger]

Thanks for the information. I was using this table from Haflinger Technik http://www.haflingertechnik.com/ftp/tec ... pdfs/3.pdf After the heads have time to settle in and before I do the tappets - I will loosen the nuts and retension to 21 - not a lot of difference but I will go to that torque.

Kerry - ring gap is fine. The Mahle piston, ring barrel set is a matched kit so the rings are already a correct fit - nevertheless was tested and clearances were all OK.

Cheers

Garry