Low compression

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heinkeljb
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Low compression

Post by heinkeljb »

For all that my engine starts and appears to run nicely, I have been having a few starting issues recently.
So I have refurbished the stater solenoid as that was sticking. I am going to dismantle the Dynastart to check the brushes and commutator for wear etc. I thought I would just do a compression check when I finished doing the oil change to SAE30.

Big mistake!!

The right hand cylinder hardly registers at all!
The left hand cylinder reads about half what it should at ~ 50 psi!!

So it looks like I have been driving around with less than half the power I ought to have.....

That's the background, now come the questions:-

There is the trick of putting some oil in the bores to see if the lack of compression is due to rings or valves, but that is for bores which are vertical - does the same trick work with horizontal bores?

Given that I shall have to dismantle things to correct the issues, how much do I have to take off?

Can I just remove the lower and upper tin ware and take heads / barrels off with the engine in place or is it easier to take the engine out?

Are barrels and piston rings in oversizes available or am I going to have to mess around with VW ones?

As this is one of the last engines supplied by PM Ward (didn't even have an engine number stamped on it) I would like to try and keep it original - but not at the expense of having to wait forever to find original barrels and rings!

Is this going to be a pig of a job?

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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pathfinder700ap
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Re: Low compression

Post by pathfinder700ap »

Hello John,

it will be definitely easier to pull out the engine first and then start with the dismantling. Pulling the engine out doesn't take long anyway.
My feeling is that oversize pistons and rings should be available somewhere. I guess the barrels should be reuseable if you remachine them to oversize (except there is heavy damage on the inside surface). I don't think that putting oil in the combustion chamber will tell you something in this case.

Kind regards,
Constantin
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Julian B
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Re: Low compression

Post by Julian B »

John, as Constantin says, removing the engine doesn't take long - certainly less than an hour subject to no nuts being jammed etc. I have done it several times now and would be more than happy to come down one afternoon to help you. A second pair of hands certainly makes life much easier.

If you want your cylinders re-honed etc, I found a good place in Newhaven last year. They can also re-seat valves etc.
Julian B
W Sussex, UK

| '62 Early Series I SWB | '72 Series II LWB |
| '56 Citroën Traction Avant |
walderse
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Re: Low compression

Post by walderse »

John,
Has Lurch been burning oil/smoking when your drive? If so, the low compresssion can either be the cylinder bore seal(worn rings) or worn valve guides with inadequated valve-to-valve seat seal. If no smoking has been occuring, the likely cause is worn valves not sealing the cylinder in compression.

First, it is best to take the engine out. Life is much simpler when you unrestricted access.

Second, using the oil in the cylinder to test compression will work just as well in a horizontal as in a vertical oriented cylinder. In the oil burning scenerio, the oil in the cylinder should increase compression over baseline whereas it will have no effect on sealing up valve guides. It could however give a bit of a seal to a slightly abnormal valve-to-valve seat interface. If no oil has been burning, the valve-to-valve seat junction is the culprit. Valves could be worn or, on the 0 psi cylinder, stuck open or even broken.

I cannot think of anything giving these symptoms that will not require moderate engine disassembly.

Oversize pistons and rings are available from a couple of different sources.

Hope this helps.
Take care.

Jim Molloy
Waldersee Farm
http://www.northwestmogfest.com
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heinkeljb
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Re: Low compression

Post by heinkeljb »

The engine starts and runs beautifully with no indication that anything is wrong. There is the vaguest of blue tinge to the exhaust gases, but nothing more than I would expect from a old engine with indeterminate service history.

If it is going to be that much of a task - taking the engine out, then it can wait until one of two things happens; it really require immediate attention or the weather improves! Nothing worse than HAVING to do major engine work in the cold and wet and possibly dark conditions.

Many thanks for the advise - sounds like engine out is going to be the better option.

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

What are your spark plugs telling you - this is an indication of oil burning.

My engine burns oil on start but not when running. When I had my haffie engine for work the mechanic said I had no compression on the left cylinder.

When I got home I put my screw in compression tester on and tested the good cylinder first - 115psi which seems about right. I then tested the bad cylinder and got 90psi. I then did a wet test and got 110psi which is getting up to where it should be.

One thing I have not done yet is check the tappets - if too tight so a valve is staying slightly open compression could be down HOWEVER the wet test shows it is bore/ring related as if it were valves compression would still be down.

So - John do a wet test as that should give you the pointer as to where to look further.

Garry
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heinkeljb
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Re: Low compression

Post by heinkeljb »

I will do a wet test today, I was unsure if it would work on horizontal cylinders as the oil will pool along the bottom edge of the piston rather that spread round the ring gap as it would in a vertical cylinder.

The spark plugs are actually as good as I would expect from any good running engine. They are the correct colour in the centre and a bit black round the edge but certainly not oily or sooty.

John
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heinkeljb
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Re: Low compression

Post by heinkeljb »

I looked at doing the tappets today and gave up! The design of the cylinder rocker box cover with pipe bolted to it is an absolute joke!

If your engine is even a little bit dirty, taking the rocker box cover off means pulling the pipe from the rubber grommet thing which seals it into the crank case. When you go to put it back on, you are going to end up putting dirt into the crank case from the end of the pipe brushing against the edge of the grommet. Then you have to worry about it providing a good seal, unless you decide that every tappet adjustment requires new rubber grommets on the oil return pipes.

So in order to do the tappets currently, you have to start by taking off the sump guard. Then remove the lower engine tin ware. Then remove the access panel on the side of the engine bay. Then clean the engine, at least around the oil return pipe to crankcase joint and the rocker box cover. Before you can even remove the rocker box cover to actually adjust the tappets. So a job that should have taken 15 minutes has become a 1 to 2 hour job! Even if you worked fast because you have done it before it would still take you an hour to do both cylinders.

So I am going to alter mine. I have a replacement oil return pipe which I will cut between the bend in the pipe and any obstruction so I can put a length rubber hose with a couple of clips on it. That way I can just undo the clips, take off the rocker box cover leaving the pipe in place in the crankcase.

I will take some photos when I get round to doing it.

John
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Julian B
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Re: Low compression

Post by Julian B »

heinkeljb wrote:So I am going to alter mine. I have a replacement oil return pipe which I will cut between the bend in the pipe and any obstruction so I can put a length rubber hose with a couple of clips on it. That way I can just undo the clips, take off the rocker box cover leaving the pipe in place in the crankcase.
John, there is a fair amount of pressure exerted by the pipe onto the rubber seal to give it a good fit, and if you insert a flexible part into the long tube that pressure will be lost. How will you get around this? (But if you can solve this then your idea sounds like a winner!)
Julian B
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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

John - do I sense just a little negative emotion in your post :roll:

Following with interest as I have to check my tappets before too long.

Cheers

Garry
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heinkeljb
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Re: Low compression

Post by heinkeljb »

If the oil return pipe needs the pressure from the rocker ox cover to "force" a seal in the grommet in the crank case it is even more badly designed than I first thought!

If that is the case, then that can be solved by just making a single cut in oil return pipe with a junior hacksaw blade so it removes only a small amount of metal in the length of the oil return pipe. If you still need more pressure along the length of the pipe, a thin washer with the right bore and outside diameter would take up the missing metal when shoved down the rubber connecting hose.

John
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Re: Low compression

Post by Julian B »

heinkeljb wrote:If the oil return pipe needs the pressure from the rocker ox cover to "force" a seal in the grommet in the crank case it is even more badly designed than I first thought!
In my (limited) experience, one has to apply a fair degree of pressure on to the rocker box cover before you can even start to wind the rocker box cover nut onto the long stud, and then when started one continues to squash / deform the rubber seal to quite an extent. I really can't imagine that replacing a section of the return pipe with a length of plastic tubing will work. (Forgive me if I misunderstood your original idea).
Julian B
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heinkeljb
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Re: Low compression

Post by heinkeljb »

The idea is that you don't have to pull the pipe out of the grommet in the crank case in the first place therefore not requiring the effort to put it back in!

Another thought is to get hold of a pair of rocker box covers and have them "altered" to have either one or two "inspection hatches" put in which would mean all you have to do is take those off and you have access to the tappets. Would be even easier than cutting the pipe!

Anyone got a pair of rocker box covers I can buy?

John
Haflinger 703AP LWB 1973 - (Once owned by Lady Sutherland & Sons.) Now called "Lurch" !

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Julian B
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Re: Low compression

Post by Julian B »

John,

The grommet fits on to the base of the pipe, held in place at the upper end by a flange. As soon as you undo the central stud holding the rocker box cover (RBC) on to the cylinder head the grommet will "push" the tube away from the engine casing. Whilst I fully understand why you would like to be able to remove the RBC without removing the pipe from the engine casing, I remain unconvinced that putting a flexible element in to the tube will work.

But then again, my engineering skills are very limited :D
Julian B
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heinkeljb
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Re: Low compression

Post by heinkeljb »

Julian,

Having not taken the rocker cover box off myself, I bow to your experience that the rocker cover box exerts pressure down the oil drain tube and will probably leak like a sieve if I attempt my first idea of improving access to the tappets.

So;

I have come up with another way to achieve the same end of being able to adjust the tappets without having to dismantle so much.

For this idea to work, it involves making 4 holes in a rocker box cover. Two larger holes corresponding to the tops of the valves so you can get your feeler gauge blade in there. Then two smaller holes, big enough to allow a socket or box spanner of the right size for the nut on the tappets.

These holes you would then tap to take something like the following:
possible solution for rocker box.jpg
possible solution for rocker box.jpg (55.65 KiB) Viewed 2031 times
I know the rocker box cover it thin, but using some thing like liquid metal epoxy resin or getting them Ali - welded to allow more thread / flat surfaces for the screw in covers to hold on to. (P.S. don't forget there will be rubber "o" rings / gaskets on the items in the picture)

Maybe this would be better for the ones over the tappet adjusting nut.
poss rocker cover new adjuster cover.jpg
poss rocker cover new adjuster cover.jpg (12.2 KiB) Viewed 2030 times
That way, all you have to do to check / adjust the tappets is undo 2 inspection covers on the bodywork, 4 covers per cylinder head and adjust what ever is need. When you are done, screw the covers back in place, put the inspection covers back on and you are done. Half an Hour Max!

John
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Julian B
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Re: Low compression

Post by Julian B »

Just thank your lucky stars that you have a Haflinger with removable engine bay side panels! The early ones (like mine) don't, making access to the tappets much harder!
Julian B
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heinkeljb
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Re: Low compression

Post by heinkeljb »

Julian,

No wonder you have so much experience of taking the engine out! :lol:

For early Haflingers then:

1: remove sump guard
2: remove bottom engine tin ware
3: clean engine - minimum around the oil drain pipe to crank case joint
4: remove rocker box cover
5: adjust inlet tappet from above
6: adjust exhaust tappet from below - watch out for the oil drips in your face!
7: do the same for the other side
8: struggle to get rocker box cover back on, drop nut several times and have to start again each time!
9: refit bottom engine tinware
10: refit sump guard

Just enough time to get to the pub for last orders!

Just remembered;
the repair manual I have states 0.15mm for both inlet and exhaust valve gaps.
the operator handbook states 0.20mm for both!

So which is it? Or do I go for something in between?

As Gary pointed out, I am currently gripping about Lurch as things are not right and taking a lot of effort to put right! :? :roll: :cry:

John
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AustHaflinger
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Re: Low compression

Post by AustHaflinger »

heinkeljb wrote:As Gary pointed out, I am currently gripping about Lurch as things are not right and taking a lot of effort to put right! :? :roll: :cry:

John
Just be thankful you have a nice cool climate to be doing this work in - we have a terrible climate where it is going to be sunny and 35C this week - it is very hard to work on your car when the weather is so good :)

Garry
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heinkeljb
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Re: Low compression

Post by heinkeljb »

I had two cheap compression testers (£10) a piece from county fair stands. Having used both, the one not appearing to work as well as the other. I chose the one that appeared to work the best and was using that to post up my comments about low compression.

As neither appears to be terribly good / accurate, I decide to buy yet another more expensive compression tester (£20 out of Screwfix). That way, if it also showed low compression I could believe there really was problem with my engine. (It starts and runs well, the plugs are the correct colour, so I didn't really think there was a compression problem)

Using the new (Screwfix) compression tester, I get the following readings:-

Left hand cylinder (1) = ~115psi
Right hand cylinder (2) = ~ 105psi

In other words - nothing wrong with the compression! (Just the testers!)

I didn't bother to stick any oil down the bores this time as the pressures are not likely to change much from the above.

I still need to do the valve clearances, but that will have to wait until the rain stops as there is too much dismantling to do in the open air - cold - wet lying on your back or otherwise contorting yourself to see / feel the gaps!

John
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walderse
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Re: Low compression

Post by walderse »

John,
It must come as quite a relief knowing that all your concerns were based on information gathered with less than optimal measuring devices. This is an excellent learning point for all of us. Cheap diagnostic tools can lead to very expensive consequences.

I understand what you are trying to accomplish by adding access ports to the existing valve covers to avoid the removal of the complete valve cover but am at a loss to understand why one would go to so much trouble. The valve cover is retained by a single M8 nut. Removal and re-installation of the standard valve cover gasket with its oil return tube is a very simple proposition. There is a small degree of attention to detail required for refitting but no more than any other work on there engines.

In order to obtain adequate thread engagement of both large and small access fixtures you have shown above will require building up a significant amount of aluminum on the exterior surface of the valve cover. These raised areas will then require thread tapping and the mating faces machined true to ensure tight sealing. Tightening and loosening these ports will likely place rotational forces on the valve cover/valve cover gasket/cylinder head mating interfaces for whcih they were never designed. The same holds true for the two mating joints of the valve cover oil return tube (at the valve cover and the crankcase). Leakage from the original sealing sites would be far more likely.

With that said, I am sure you can locate a pair of valve covers from any of the current parts dealers. A set of ventilated valve covers are available here:
http://www.puch500.at/?action=tuning
Plain ones occasuonally come up on eBay but that is a hit and miss proposal.
Please keep us informed as to your progress and the overall cost of this modification.

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