Low Compression in third cylinder

[toastman]

why not do a leakdown test before taking the motor apart?

Donald

[Twoth]

why not do a leakdown test before taking the motor apart?

Donald

Yea thats a good idea too. I just figure if I'm going to take the head off anyway, I can get a valve job and change the head gasket. If I can throw a tool together to do a leak test I may just try that however first.

[GreyGhost]

Yea thats a good idea too. I just figure if I'm going to take the head off anyway, I can get a valve job and change the head gasket. If I can throw a tool together to do a leak test I may just try that however first.

Princess Auto occasionally has a Leakdown tester dirt cheap.

[AlexF4i]

If its a simple thing like cabon build up on the valves that are causing the #3 valves to not seat properly I would definetly try running a can of combustion chamber cleaner through it first. Try and have the motor fully warmed up and running when doing this...its much more effective when the engine is hot.

[Twoth]

I was already in there so I took the head off and took it to a shop. I'll let everyone know what happened when I pop everything back on.

[Twoth]

So I ripped the head off and took it to a shop for a valve job and the guy quoted me 800 bucks... which is way more than I'm expecting to spend. I think 200-250 is reasonable, does anyone have any experience with any shops around toronto that could do it for that much or am I low balling the expected cost.

[sircastic]

Why does it need a valve job? What's the cause of the low compression? I wouldn't go spending any money on a 'valve job' without knowing the cause. If you take to a shop for a valve job they will do just that but it might not solve your problem.

A quick check ... if you have the head off (assuming cam(s) are out) lay the head level and upside down and fill each combustion chamber in the head with windshield washer anti-freeze ... don't spill any on the head. Check it a few hours later ... or in the morning and if the number 3 cylinder has a lower amount in it you know there's a problem with the valves sealing or a crack in the head. Look in the exhaust and intake ports (or coolant jacket) and see where the windshield washer fluid went.

[BrianZ]

So I ripped the head off and took it to a shop for a valve job and the guy quoted me 800 bucks... which is way more than I'm expecting to spend. I think 200-250 is reasonable, does anyone have any experience with any shops around toronto that could do it for that much or am I low balling the expected cost.

The cost is dependant to a large extent on what needs replaced. Replacing valves can add up the cost quickly. Did the shop give you a breakdown on parts and labour? Out of curiosity, how many kms on the bike?

[boyoboy]

So I ripped the head off and took it to a shop for a valve job and the guy quoted me 800 bucks... which is way more than I'm expecting to spend. I think 200-250 is reasonable, does anyone have any experience with any shops around toronto that could do it for that much or am I low balling the expected cost.

gord bush in etobicoke. highly recommended, and built top running superbikes in the 80's.



you don't fool around. engine apart already? i once had the same prob you have, shop told me i had "burnt valve(s)". the cylinder that was low, had, get this, 70psi.
later, at home, i found a tight valve on the cyl in question. this was immediately after paying for a valve adj. at the same shop. hmmm....

SOME shops, in order to save time, just adjust the valves for excessive lash. they do not want to go through the bother of adjusting tight valves. the valves that tighten up are usaully on engines that spend most of their time approaching redline - which basically hammers the valves into the seats and tighten up the lash. if left tight, the hot gases escapng by the valve will eventually burn it.

anyway, in my case, i adjusted the tight valve in question, and presto - full compression!

i've been turning my own wrenches since...

[Twoth]

The bike has 34K on it.

I'm going to get my head back and try the fluid trick first to see if maybe it is a seating problem.

For the tight fit valve, how could I check for that? I don't have a valve spring compression tool, which is primarily one of the reasons I thought I could throw it at a shop for a quick check and clean.

The cost from that shop (800) was just an approximation of how much he thought it would cost, no breakdown.

[RonnieRev]

If you are on a tight buget, just have the machine shop repair the
valve(s) for the clyinder that is causing you the problem

[djltoronto]

For the tight fit valve, how could I check for that?

You already did, in post number 1... you said you did a clearance check, and none of the valves had 0.00 clearance!

[NP6000]

I don't like to preach, but you keep asking for help and never follow any of the recommendations. If you had done a leak down check way back when instead of removing the head you would be far better informed about how to proceed.

Right now your playing an expensive and time consuming game of guess and check - and it could have been avoided.

Again, what lead to the conclusion that the head needs a valve job?

[fugue]

Notwithstanding the OP's issue, I'm curious to see - how would you all diagnose the following?

Numbers from an actual motor:

Cyl. Leakdown Compression
1 1% (rings) 150psi
2 2% (rings/exh) 140psi
3 1% (rings) 110psi
4 3% (in) 155psi

Nominal compression for the motor is 138psi, minimum is 109 (from the service manual).

[boyoboy]

You already did, in post number 1... you said you did a clearance check, and none of the valves had 0.00 clearance!

just for clarification:

you can have a measurable valve clearance greater than zero, but less than specified for the engine, and still have some loss of compression. HOW? as the motor warms up metal expands. this may result in the valve not completely closing as the engine heats up to operating temp.

the valve clearance specifications are normally done cold, and the manufacturers have taken into consideration the expansion of the metals when determining the clearance.



but i cannot say for sure this is what has happened in your case. I think you jumped the gun a little bit when you pulled the head off. one poster mentioned having just the one cyl in question worked on by the machine shop. worth considering.

[boyoboy]

i would recommend you give gord bush (machining) a try. he has a fantastic rep with bikes, is honest, and extremely capable. he has previously worked for honda canada, and was also crew chief for Michael taylor (CDN SBK champion) located in etobicoke.

check out his website. gordbushperformance.com

[Twoth]

I don't like to preach, but you keep asking for help and never follow any of the recommendations. If you had done a leak down check way back when instead of removing the head you would be far better informed about how to proceed.

Right now your playing an expensive and time consuming game of guess and check - and it could have been avoided.

Again, what lead to the conclusion that the head needs a valve job?

I don't recall asking for help multiple times, I brought up one issue and then mentioned what I'd done and that I'd already taken off the head. I was unaware of the leak down test and I've acknowledged that mistake.
I haven't brought back my head from my brother's place so I haven't had a chance yet, but I am going to try what someone previously suggested and put fluid on the top of the cylinder with the head upside down and see if it leaks through.... and I believe I mentioned that.

I thought it was a valve clearance issue due to the compression test.

[djltoronto]

just for clarification:

you can have a measurable valve clearance greater than zero, but less than specified for the engine, and still have some loss of compression. HOW? as the motor warms up metal expands. this may result in the valve not completely closing as the engine heats up to operating temp.

I am assuming he's doing a compression test on a cold engine! which has greater than zero for valve clearance, which would conclude that it's not the valve clearance causing low compression in his case.
If the compression test was done on a hot engine - then as you say, valve clearance may be the only issue.

[toastman]

perhaps the compression test was not done with the throttle held wide open.

Was the bike running poorly?

[toastman]

I went back to the first post and I don't see where you posted that the bike was running poorly or misbehaving.

It's possible that the compression test didn't work due to the throttle not being held wide open and during the test that there never was a problem with the bike.

Donald