Low compression + grey smoke

[Irtron]

Hi everybody.

I have a 1994 vmax with 35000 miles on the clock that suggests it's time for some maintenance

I bought the bike last autumn as you can tell from my vmf join date.

Immediately I noticed greyish smoke from the exhaust when I rev up after a bit of idling at traffic light or warming up. As per my knowledge, mostly theoretical though, that usually indicates caked valve seals. So I scheduled seals replacement along with reshimming.

I checked the compression and was impressed with the readings that showed exactly what the repair manual says 10 kg/cm2 (142 psi) same in all four cylinders. Well, until I found the correct figure on the specifications page that is 14 (200) of course .
A few drops of oil to the spark plug hole - compression rises to the nominal 14 kg/cm2 at once. Again the theory suggests the piston-rings-cylinder wear rather than failed valves. Considering the compression figures are very close in all cylinders.

Now I have the engine dismantled and disassembled for inspection. Here are the photos.

1. Head gasket.
The first surprise - corroded head gaskets. Both have through holes in outer layers on both sides.
There is no sign of blown gasket though. And the middle layer survived the attack.
Is this normal thing or someone used acid for coolant?

2. Piston/Cylinder
Now I got really impressed when I removed the pistons. Both piston and cylinder surfaces still have machining on them except for a bit of glazing on front-back cylinder walls about 1 inch wide. Even glazed spots still have machining pattern on them. The measurements, first cylinder:

76.00 d1 top front-back
75.99 d2 top left-right
75.99 d3 mid front-back
75.99 d4 mid left-right
75.99 d5 bottom front-back
75.99 d6 bottom left-right
75.95 piston
0.04 top ring side
0.04 2nd ring side
0.54 top ring gap
0.55 second ring gap
0.90 oil ring gap

piston and cylinder - no wear whatsoever. After 35K miles! How is it possible?

3. Piston rings
gaps - out of limits.

Also I noticed that the ring gaps were aligned with each other rather than being criss-crossed. The piston has the carbon deposited on one side only.

Can a bit of ring wear cause such a dramatic loss of compression? Or it was likely something else like stuck rings? Or valves?

4. Piston pin.
The top bearing surface looks dodgy. Although micrometer doesn't show any change in diameter and it's smooth to touch. The rod head looks ok.
Does the pin need to be replaced?

Can you guys say something on the subject? Where else to look to make sure the compression is back?

Yeah, forgot to mention.

5. Shims and seals
I replaced the seals. The old ones had really hard lip.

Also the shimming didn't go smoothly for me.
The clearances were way too tight, if not extreme, e.g. 0.20 and 0.22 for the first cyl exhaust. So I need 168 an 182 shims for them that I can't find actually. Could that affect the compression?

Cheers,

 

[davesax36]

I think you might deserve some sort of award for this first post. I'm thinking "Most thorough mechanical work before posting".

I guess it's a bit late, but did you do a leak down test? You'd hear whether it was leaking across the cylinders, back into the oil pan, or out a valve. Valves out of spec can cause compression to be out of whack. Although I have limited knowledge of this subject, I find it hard to believe that all cylinders would still read so close if it was a valve issue. I'm not sure I can help, but welcome to the forum. Someone will be along soon that's had these motors apart. They'll be of more assistance.

 

[naughtyG]

Head gaskets look a bit shit, new ones should help!

shimming sounded normal - valve clearances to get tighter over time on these engines.

Looking at your writeup and photos, I'd say ring wear could be your main problem, but I'm no real expert.

You want to get answers from Sean Morley really, and he can also hook you up with whichever shims you need.

 

[MaxMidnight]

Did you notice it using much oil before the tear down?

As you say there is nowt wrong with the bores and the pistons seem OK as well.
I'd be inclined to do a glaze bust and replace the piston rings & valve stem seals.
Check the valve seats and if necessary lap in. Adjust valve clearances as necessary.

Suspect the motor has been run without anti-freeze (corrosion inhibitor) which has caused the erosion of the head gasket.

 

[sdt354]

Ring gaps should always be staggered when assembling. A poor man?s head check is to flip the heads upside down and fill the bowls with gas. It should hold over night. 35k isn't a lot of miles for a Vmax.
Once a year I steam clean my valves. Many moons ago,(when dinosaurs roamed) in tech school, I was lucky to have some great instructors. One thing we got into (everything was hands on back then) was pouring a small stream of water into an engine at high idle. One guy swore by ATF fluid, but water works well for me. Yes, right down each carb throat. Let the engine evaporate all the water before shutting down. When done, I pull an exhaust pipe or two and get a peek at the valves. The carbon build up is gone. Running high test in a stock engine, rich jetting/settings, excessive idle, all build exhaust valve crud which will keep you from running at peak efficiency.
Steve-o

 

[davesax36]

Will anything happen to the intake valves with the water treatment? I see how this is steam cleaning, but how much water are you talking about? I'd love to see my valves clean.

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[Irtron]

Did you notice it using much oil before the tear down?

I added the oil couple of times about half to three quarters a litre per 1000 miles I think. I wasn't warned too much as I was already aware of the engine burning a bit of oil anyway.

Suspect the motor has been run without anti-freeze (corrosion inhibitor) which has caused the erosion of the head gasket.

You mean fresh water rather than glycol? When I changed the coolant the old one looked rusty indeed. With quite a lot of hard particles in it when I used tap hose to pour through the block and rad.

 

[Irtron]

Ring gaps should always be staggered when assembling. A poor man?s head check is to flip the heads upside down and fill the bowls with gas. It should hold over night. 35k isn't a lot of miles for a Vmax.

Yes, I planned to go to local B&Q to get some kerosene to do the leak test. A bit cautious to leave the petrol pouring around overnight.

One thing we got into (everything was hands on back then) was pouring a small stream of water into an engine at high idle.

Wouldn't water cause some warpage to the valves? I can imagine it's rather safe on bulky parts like piston or head, but small superheated due to little heat removal exhaust valve will definitely take quite a shock with rapid cooling?

 

[bazwell]

I'm impressed. Well done.

The head gasket looks like it has been without good anti corrosion inhibitor. No biggie, as long as the water jackets in the head don't appear to have any corrosion. (I don't see any)
The head gasket doesn't appear to be blown. I think that side of things is OK.

To me, the pictures aren't showing anything unusual, but there is a couple of pics which would be helpful.

i) Pics of the top of the pistons, before the carbon is cleaned off the top. You want to see black right to the very edge of the piston, like this one. http://i710.photobucket.com/albums/ww103/padmei_crayfish/58201244.jpg

ii) Pics of the valves, showing carbon build up. This the area I'm talking about --> http://mud4fun.files.wordpress.com/2012/08/compare_valves-1a.jpg


If there is a clean area at the edge of the pistons (ie - NOT black dusty carbon right to the edge) then the rings aren't sealing. If the pistons and bores measure OK, then it could be just the rings that need changing. (You must change big end bearings at the same time as rings.) You need to be familiar with measuring pistons to have the right "feel". Pistons are often measured at 90 degrees to the gudgeon pin, level with the pin. Pistons are oval, and tapered! It is possible that an experienced engine builder will get different measurements to you.

If there is a carbon build up on the back of the valves, this would be because valve stem seals aren't sealing. This could be because the valves or valve guides are worn. Experienced head machinists usually have a "feel" for this one also.

From what I have seen, I think that you could be in luck with this motor. If you use new gaskets and seals, rings, big end bearings, and get the heads serviced it will be like a new motor!

 

[sdt354]

Will anything happen to the intake valves with the water treatment? I see how this is steam cleaning, but how much water are you talking about? I'd love to see my valves clean.

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I've done it on all my bikes and trucks. I'm talking a trickle feed, maybe 1/4 cup or so.My Bro inlaw likes to spray a mist when he does it.

 

[Traumahawk]

I done it with ATF if my cars....Let me warn you...you are definitely FOGGING for mosquitoes after that.

 

[sdt354]

Yes, I planned to go to local B&Q to get some kerosene to do the leak test. A bit cautious to leave the petrol pouring around overnight.

Wouldn't water cause some warpage to the valves? I can imagine it's rather safe on bulky parts like piston or head, but small superheated due to little heat removal exhaust valve will definitely take quite a shock with rapid cooling?

Never had an issue with warpage. Ice cold Gumout is used with no issue, though I'll amitt its atomised.

 

[06VMAXIMUS]

I've done it on all my bikes and trucks. I'm talking a trickle feed, maybe 1/4 cup or so.My Bro inlaw likes to spray a mist when he does it.

Never done it on a bike, but it is true that it works. I have always used a spray bottle to mist the water in the carb. You def. don't want to pour a large amount of water into a running engine all at once due to the fact that water does not compress well, and could bend a rod.

 

[gamorg02]

Never done it on a bike, but it is true that it works. I have always used a spray bottle to mist the water in the carb. You def. don't want to pour a large amount of water into a running engine all at once due to the fact that water does not compress well, and could bend a rod.

or worse someone could do this:

http://mustangforums.com/forum/5-0l-general-discussion/368307-im-done-with-this-car.html

 

[sdt354]

or worse someone could do this:

http://mustangforums.com/forum/5-0l-general-discussion/368307-im-done-with-this-car.html

Yea, that might be a bit too much water in the wrong place.

 

[Irtron]

A poor man’s head check is to flip the heads upside down and fill the bowls with gas. It should hold over night.

Tried the 'leak' leak test today. The kerosene is gone through the valves in less than couple of hours. Fail, apparently.

i) Pics of the top of the pistons, before the carbon is cleaned off the top. You want to see black right to the very edge of the piston

Got the picture. I didn't post it initially because didn't think of any importance of it. Thanks

ii) Pics of the valves, showing carbon build up.

Ok, I'll get them out.

ii)If you use new gaskets and seals, rings, big end bearings, and get the heads serviced it will be like a new motor!

Thank you very much for reminding me of the bearings. I've ordered all the stuff, will get the parts by the next weekend if I'm lucky.
It was rather tricky to read the crankshaft numbers with a dentist mirror and a torch but I managed
The crankshaft - 11 2332, all four rods - D7 that makes all the bearings the same #6 pink, right? I found 1FK-11656-50-00 here in the UK.

So it looks like the valves are responsible for both excessive oil burn and low compression. I'll post some pictures as soon as I take them.

Thanks everybody for you comments and suggestions. Great help for me indeed.

Edit.
2bazwell
Very good point with the piston edge carbon. Looks like the rings add to lowering the compression figure as well.
Thanks man.

 

[Irtron]

Suddenly...

There is another problem.

I have difficulties with getting one of the chain guides out. I removed the rear block guide no problem - click, pull, slide up smooth and easy.

However the front block guide was sitting very tight so I had to knock it out with a hook tool. It popped out about an inch and now it refuses to move and it fills like if I apply more brute force it's likely to break.

I'm not sure the guide will slide into the socket if I just push it back. What could be the problem?

 

[bazwell]

2bazwell
Very good point with the piston edge carbon. Looks like the rings add to lowering the compression figure as well.
Thanks man.

I agree. The carbon on top of the piston is quite thick and oiley, but the edges are pretty clean. Given that you said the ring end gaps had opened up, I think that you have a little from rings and a little from valve guides.

The kero test on the valves can sometimes appear worse than it really is. No doubt there is some problem, and that you could do with re-seating the valves, but with a thick carbon build up, the carbon itself could be holding valves slightly open.

Good luck with it all.
I'm no help on the chain guide question, sorry.

 

[Irtron]

Sorry for being sluggish on updates. Still waiting for the rings and pins from partzilla that I ordered two weeks ago. They sent me an email last Thursday that everything is ready for shipping except for the rings that are scheduled for delivery on Wednesday - the day before! Nothing from them since

Anyway.

I did more leak tests kinda in opposite direction. I.e. I poured the kerosene into intake and exhaust channels on the front and back of the head rather than in the chamber.

Exhaust valves stayed dead dry for 24 hours all right all four cyls, no liquid escaped.
Intake 1 and 3 - dry, 2 and 4 became wet, level dropped about half inch over 24 hours.

Finally I took the valves out today:

1. All the seats look pretty much the same.
2. Carbon deposits on all intakes except for 2nd cyl.
3. Burnt deposits on 2 and 4 exhausts. This is a bit of surprise. So I had a more thorough look at their chambers -
4. 2 and 4 chambers have clear area on intake side. Piston counterpart surface is clean too.

That makes me suspicious about the head gaskets. Perhaps they bled some coolant into the cylinders that cleaned the carbon as per sdt354's suggestion. This is just a speculation though.

Although the coolant was clear and looked like new after 2000 miles since I changed it, neither oil contamination nor white smoke. I refilled the coolant once though but I thought it was because the hoses leaked a tad due to old rust.

Do you guys have any idea why there is such a difference in the pattern when all cylinders had the same compression and the same wear condition?

Cheers,