Compression Data for 1750 Engine

Any body got the compression data for a 1750 Engine. It seems I might have a bent Valve, I need to get it confirmed with a compression test.
Help......

I would have thought that doing a wet and dry compression test would give you the answer you are looking for without the need for any compression data from an engine in excellent condition.
Because what you are looking for is a low reading that is independant of bore wear

I don't know what it is Mitch but I'll have a look in a book tonight.
Stori's right though - you are looking more for a comparison between the others than an absolute value.
What makes you suspect a bent valve?
Have you been revving the nads off it again?

Don't you have a spare engine in your shed?

Ok I am showing my ignorance here, I took it into the Garage next door to work, to have him try to balance the carbs, as I thought that was the cause of my slow running problem. He reckoned I have one or possibly two bent Valves, this is the cause. It seems beause they aren't seating properly the back pressure is not right, hence the slow running problem. It sorts itself out at higher revs, but I am probably loosing power.
In order to check if they are bent, he said he needed to do a compression test but didn't know the correct values. The Brooklands book doesn't seem to give it. I have just bought Pat Braden's 'Bible', but I haven't found it in there yet.
I can see where you two are coming from, but I am just going on advice ATM.
No Rick haven't revved it too much, alegedly they are prone to it??. I have a reciept for a repair of a bent Valve, from 1997, at about 6000 Miles ago, perhaps there is something out of kilter somewhere
I do have the spare Engine, so it might be I swap the heads over, but it depends on reletive conditions.
I can feel a pain in the Wallet coming on.........

Sounds a bit funny.
Do you know if the block or head has ever been skimmed?

Doesn't have to be bent valves for them not to seat.
Could be worn guides or valve seat recession?

I have a compression gauge if you want to borrow it.

No Rick haven't revved it too much, alegedly they are prone to it??.

Oh! Are they? I thought it was the drivers....

Checking the History, it all gets very confused, the original Engine was taken out in 85, rebuilt and put back in, in 87. During that time the spare Engine was used. It seems the original Engine had it's Head skimmed, and the seats re-cut before it was put back in the Car.
Then in 1997, No 3 exhaust valve was found to be bent, the reciept mentions stripping the head, but also stripping the head off the spare engine to inspect, so it isn't clear if they put that head on or the original after reseating the Valve...
So I could have a Bent Valve in BOTH heads....

Thanks for the offer of the tester rick, I will let you know. I need to consult with my mechanicaly minded Father first.

Can't find any useful info in my books.

Just one thing that did come to light - do you have the winter/summer lever for directing warm air to the carbs?
Worth checking it's on summer!

Mitch...

you only need a comparison between cylinders to tell if something is broken or bent. If for some reason theres one cylinder being out; Have the mechanic perform a "leak test"(*) before he strips the engine down.

Hoygs

(*) Leak test= blocking the flywhell with the piston at TDC and closed valves, then applying compressed air through the spark plug hole and listening for any possible way of the air evacuating the combustion chamber. IE through dipstick (piston), exhaust(valve), carb(valve) or header tank (head gasket)

I don't think you'll find compression data anywhere since, as was said before, the numbers are not absolute but rather just a comparison with each other. Cylinder pressures within 10% of each other is considered normal. No disrespect here but I'd think that the Garage should know that. Keep in mind that for good test results, valve clearances and cam timing must be in spec, all the sparkplugs must be removed and the throttles held wide open.
Having only one bent valve is extremly unusual too. Cam timing is the usual cause for bent valves in which case all four valves on the affected side would get bent, not just one. Perhaps the valve is burned and not bent?

I have recently done a compression test on my MK2 1750GTV as it has been stored for ten years. From memory th readings were about 110 (psi i think) and all cylinders were within about 5% of each other. I will double check and let you know.

James

Thanks Guys, I probably lost something in my translation between what was said, and what I wrote. The guy is aware that it's the differance which is important, but he wondering if was possible to check it against standard spec. I have given him the 10% differances, and mentioned the 110psi, as a guide.
He also agrees that it is more likely to be burn't than bent, but it is strange that it has bent one before and it, by chance is the same one, No 3 Exhaust. He thinks No 1 also may be suspect.
No 3 has allways seemed slightly noisy whilst I have had the car, so it is possible that it has been badly adjusted when it was fitted, and the impact of it closing hard has damaged the seat.
Next step is to get the compression test done, and strip the spare engine to check the condition of that head. It might with luck be just a case of cleaning it up and swapping them over. He says optomisticaly....

Think the bloke is OK, not an Alfa specialist, but race prepares M3 BMW's for the single make touring car racing.
should know the basics then....

Oh the joys.

Good luck with it Mitch!

Tell him you need it back for GONAD on August 15th!!!

I guess 110 psi would be OK for a closed throttle comp test but not for an open throttle test. For an open throttle test, expect to see like 140-150 to as high as 200 psi. The wide range, and the reason there's no specific number, is because of all the variables like valve clearance, cam timing, cam profile, battery, starter and cable condition, coked chambers, skimmed head, etc. that all play a role in static compression readings.
The two most common causes for burned valves are insufficient valve clearance and/or a weak mixture. Since only loose valves make noise, and with yours being slightly noisey, that would seem to rule out a valve clearance issue (although a worn cam lobe and/or follower could cause the noise too). So if the valve is burned, for a second time, I'd suspect the root cause to be fuel mixture related.
Good luck!!

The 110 compression test was with the engine off and all the plugs out just cranking it on the starter.

James

Well eventually got the test done, the Garage had a Fire in the Fuse box, which took out the Electrical system, and ours at work...

So after all that it's fine, 155 Psi in number one, 160 in the rest....

So it is the Carbs, which is after all what I and most other people said it was. It does seem to be a bit more than just adjustments though, maybe the rubber mounts are leaking, which is affecting the air intake balances. Next step is to find a real Weber expert, anybody any recomendations, Yorkshire area, Alwyn Kershaws, and a guy called David Bogg in Malton are my thoughts at the moment.

Mitch,

Lean on the carbs with the engine running. That'll stretch the rubbers and you should be able to hear a hissing sound if they're leaking.