Lost compression to #1, but no clue what the issue is

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audiocontr
Canada
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Lost compression to #1, but no clue what the issue is

Post by audiocontr » Sun Jun 21, 2020 3:25 pm

I believe i over revved the engine from trying to take a decline in too high of a gear. It was very strange. Normally the little truck will handle a descent just fine under its own gearing. This time it reved really high and i quickly clutched and braked. I noticed the engine sprayed oil all over the back of the truck.

I was running off of 1 cyl from that point forward

No compression in cyl #1. Leak down couldnt hold enough air at TDC. I put 40# of air pressure directly into the cyl and it escaped via the crankcase.

I pulled the cyl off and everything is fine. No issue whatsoever. Rings look fine. No bent valves (that i can see). no impact points. No bent pushrods. piston looks awesome. Nothing. I'm stumped!

I guess i will put it back together and try again. Speaking of which, do i need to have the head to cyl mating surface machined? It looks ok, but i cant imagine how it holds compression without a gasket!
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

Heinkeljb
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Re: Lost compression to #1, but no clue what the issue is

Post by Heinkeljb » Sun Jun 21, 2020 3:54 pm

If air leaked to the crankcase, then it can only get there down the barrel! So if the piston does not have a crack in it, the barrel is not scored, then it must be that the rings don't fit! Possibly you managed to get the gaps in the rings to all line up, but more likely you just have worn rings / barrel.

Head to barrel seal is plain - no gasket, so make sure it isn't dinged anywhere.

John

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audiocontr
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Re: Lost compression to #1, but no clue what the issue is

Post by audiocontr » Sun Jun 21, 2020 5:00 pm

Jim L rebuilt it for me a couple years ago. Rings are "new"

I agree with your logic. Guess its time to check for gap spec on the rings. This was a sudden change, not a gradual one... just weird!
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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rmel
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Re: Lost compression to #1, but no clue what the issue is

Post by rmel » Sun Jun 21, 2020 5:22 pm

If the Exhaust valve seat receded you may not hold compression.
Possibly absorbed all the clearance at the rocker thus being held open.
Since you already pulled #1, I suggest you check the gap for the
other 3 and see if they are tight -- might be a clue.

As far as the head to jug seal goes, the best practice is to hand lap
the head to the jug. Way I do that is jug in a large vise, a bit of lapping
compound on surface then rotate the head in place back-and-forth until
the head surface shows uniformity. You do need to prep that surface for
a proper seal. Lapping compound can be had at Napa.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

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audiocontr
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Re: Lost compression to #1, but no clue what the issue is

Post by audiocontr » Sun Jun 21, 2020 5:28 pm

Thanks! I'm having a heck of a time finding cyl #3 and #4. :lol:

The hand lapping makes perfect sense. much appreciated
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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rmel
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Re: Lost compression to #1, but no clue what the issue is

Post by rmel » Sun Jun 21, 2020 6:09 pm

Dah !! Tricked by that 1/2 pint Pinzgauer again :P

Same deal though, just half the fun to rebuild.

I almost forgot, you will probably find a fair amount
of dried Permatex Aviation #3 at the jug block seam.
That will need to be cleaned and refreshed.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

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audiocontr
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Re: Lost compression to #1, but no clue what the issue is

Post by audiocontr » Sun Jun 21, 2020 7:05 pm

You are correct on the permatex. When applying, do i put a thin layer on, or significant amount?
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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rmel
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Re: Lost compression to #1, but no clue what the issue is

Post by rmel » Sun Jun 21, 2020 8:22 pm

Yes, you have to put the Permatex on a wee bit on the tick side, let it set up some
before installing the jug. The problem with Permatex is the viscosity is a bit too low,
somewhat runny, but it's OK. An alternative is Hylomar AF (advanced formula). I've
been using that recently, higher viscosity, out of the UK and used by Rolls Royce.
The original formula called Hylomar Blue requires you assemble then pull apart,
let it cure a bit and re-assemble. These products won't harden, expensive though.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

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Garrycol
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Re: Lost compression to #1, but no clue what the issue is

Post by Garrycol » Sun Jun 21, 2020 9:05 pm

While you may have revved your engine very high, it would not have over revved if in gear (even in first). Do you still have a governor? I dont and I never get anywhere near max 5200RPM.

As Heinkeljb said that if the air went into the crankcase when you pressurised it, it most likely went down past the rings. I know you checked them but check again. I have had cracked pistons and cracks around the rings. If ring gap all aligns that could cause lower compression. Also - no compression could be cause by tappet gap too tight and stopping the valve from closing. My tappets close up and in a worst case scenario do not close so loosing compression - I have had this.

Do not use any jointing compounds - the heads are clamped down on the top of the liners sealing them and as the cylinder heats up it further seals.

What I would do as you have the cylinder off. Check piston rings again, align rings so the gaps do not line up and no gaps to the bottom of the cylinder (when stopped on a side slope oil can run into the cylinder head), reassemble and redo your tappets and run - hopefully every thing will be OK.

Garry
1973 Haflinger AP700
1977 Landrover FC 101
2007 Range Rover Sport TDV6
1971 Jaguar Series 3 E-Type Conv
1957 Landrover 88" Station Wagon
1957 Landrover 88"

Heinkeljb
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Re: Lost compression to #1, but no clue what the issue is

Post by Heinkeljb » Mon Jun 22, 2020 1:32 am

Can't hurt to redo the valves with a bit of "lapping" whilst you have the bits apart. I know you said you could hear the air escaping in to the crank case, but if your ears deceived you, then the most likely places for the air to be escaping is via the valves - unless you have cracks in your cylinder head.
So now is the time to check the valves, you can turn the head upside down and pour some petrol into the bowl. If the valve are sealing then the petrol will stay there. If they don't seal well, then the petrol will seep in to the inlet or exhaust tract or both!

John

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Jim LaGuardia
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Re: Lost compression to #1, but no clue what the issue is

Post by Jim LaGuardia » Mon Jun 22, 2020 9:21 am

Head was rebuilt. Valves should be fine. Make Sure piston is not fractured under the rings. Call me, I may have rings. Doing 9 motors, let me know what bore size.
Currently setting up my lathe to repair crankshafts.
Cheers, Jim LaGuardia
http://smg.photobucket.com/albums/v510/Goatwerks/
"Arch Magus of Machines."

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audiocontr
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Re: Lost compression to #1, but no clue what the issue is

Post by audiocontr » Mon Jun 22, 2020 10:18 am

Will do. Saw your e-mail. Thanks Jim!

80MM jug. I pulled rings and they appear in great shape. Ring gap is within spec. I'll give you a call around mid day
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

Joeri
Belgium
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Re: Lost compression to #1, but no clue what the issue is

Post by Joeri » Mon Jun 22, 2020 3:52 pm

If you over reved the engine you will probebly blown out the seal on the crankchaft front or rear due to to much pressure in the engines oil reservoir . This is why it is covered in oil... the loss of compression in cyl 1 can only be 2 things..... a valve not closing or a piston leak ( pistonrings , hole or scrapes against the piston wall). All these thing are a easy fix and after that it will run smooth again.

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Garrycol
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Re: Lost compression to #1, but no clue what the issue is

Post by Garrycol » Mon Jun 22, 2020 8:24 pm

Jim LaGuardia wrote:
Mon Jun 22, 2020 9:21 am
Head was rebuilt. Valves should be fine. Make Sure piston is not fractured under the rings.
Hi Jim - yes something to look for - my first engine failure just just cracked pistons, where in the second failure was a crack in the piston under the rings. Engine ran fine on one cylinder but the other was zero compression.

Garry
1973 Haflinger AP700
1977 Landrover FC 101
2007 Range Rover Sport TDV6
1971 Jaguar Series 3 E-Type Conv
1957 Landrover 88" Station Wagon
1957 Landrover 88"

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audiocontr
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Location: Toronto Regional Area

Re: Lost compression to #1, but no clue what the issue is

Post by audiocontr » Tue Jun 23, 2020 12:43 pm

Joeri wrote:
Mon Jun 22, 2020 3:52 pm
If you over reved the engine you will probebly blown out the seal on the crankchaft front or rear due to to much pressure in the engines oil reservoir . This is why it is covered in oil... the loss of compression in cyl 1 can only be 2 things..... a valve not closing or a piston leak ( pistonrings , hole or scrapes against the piston wall). All these thing are a easy fix and after that it will run smooth again.
Hmm, interesting. It blew out from the right hand side of the engine, I suspected the oil came out of the oil fill tube. I did not find oil behind that point. I will inspect the seals. Thanks!
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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