I want to open this up to a wider audience. My engine has just come back from the shop where they have fixed 2nd gear. The gearbox is integral to the crank case and they've had the bottom half off.

The engine won't start. It turns over faster than it should and I've tracked it down to low compression - 30 to 50 PSI in each cylinder. I have spark, fuel and airflow. The cam chain has not been moved as all the timing marks line up properly. The carbs haven't been touched as they stayed here with me. I doubt very much that the head's been off.

What could cause low compression in all cylinders that could be done when working on the bottom end of the engine?

I cant answer your questions but have you tried a compression test after dropping a bit of oil down each cylinder and did you have the throttle fully open when you tested it ?

I didnt' try oil. The throttle was fully open and I had the carb slides lifted up as well.

TBH if it spins over fast it does point too ether low compression, ignition timing probs or both, you ain't having no luck are you ? Have you spoke with the repair people ? I assume your pulling your hair out, I would be, sorry cant offer any help.

probably way to obvious-but have you established if all pistons are moving?

Ooo, I hadn't thought to do that. There is compression in each cylinder, though not much. For one of them to be stopped would be very bad. How could I tell that they're all moving?

remove all plugs-insert say a pencil into each pot one by one whilst rotating engine you should feel each piston come up to tdc and then fall---do it slowly or you will snap the pencil off(also coathanger or similar)

Hi when the crankcases are split to replace gearbox there is no need to disturb the crank or cams you can leave them in situ it sounds like they have not done this and although the cam marks line up have you checked the crank mark as it looks like your valve timing is out and causing low comp
iv done loads of these and there is no reason why it shouldnt be the same as it went in
cheers malc
ps ring me if you cant find fault
07960011585

Malc,

With the T mark on the on the timing rotor pointing at the mark on the crank case, the dots on the cam shafts line up with the marks on the cam holders. The leading edge of the large tooth on the timing rotor is right in the centre of the timing pickup. Could the timing still be out?

Just a thought.

I did to 4age engines, one with the toyota desinged and cast 16v head, and one with the yamaha cast 20v silvertop head.

when replacing the timingbelt on the 16v the marks on the pully needed be alainged with the timing marks on the camcovers, but when I did it like that on the yamaha head I had the same problem asl you No compression whatsover.
although my 20v velve cover has something that can be seen as timingmarks, it turned out that on the 20v head you need to set the intake cam with the left timing mark to the cover, but the exhaust cam is timed not on the cover mark but on a second timing mark on the intake-cam-pully. although the timing cover made me think otherwise.......

looks like the toy folks cast the timing marks and yamah designed the cams and pullys with different idea of marking...

here's piccie
[img][/img]


I can't believe that the engine is so bad that there's no compression at all, so the must be a fault in the build-up, if not you have on really bad engine!

regards Thomas

[Edited on 23/10/06 by thomas4age]

If all cylnders are affected its either valve timing way way out or much more likely bent valves.

I was worried that someone would say that. My train of thought was that the pressure is held in by the valves, the head gasket and the piston rings. Its unlikely that the gasket or rings have gone on all cylinders equally, the timing seems to be right so one or other set of valves may be damaged. Or both sets.

How do I check this? Is it a head off job?

quote:

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Originally posted by smart51
Malc,

With the T mark on the on the timing rotor pointing at the mark on the crank case, the dots on the cam shafts line up with the marks on the cam holders. The leading edge of the large tooth on the timing rotor is right in the centre of the timing pickup. Could the timing still be out?

---

What's the chance of the timing rotor slipping on the crank (or being "slipped" by a mechanic)? is is splined? My boss' suggestion was that it might have been tampered with.

dunno why noone hasd mentioned it but have you rang the company that did the work about this? To find out what they did exactly?



Does it look like the head was removed (thinking could the company done a drity and swapped a head over?)

It does sound like timing. did you set this yourself in the past?

Go back to first principles and remove the top coer to see the valves. Do the pencil thing and turn the engine over to see the valves move in realtion to cylinder one - the valve opening sequence is well documented and yours weill be similar nough to show if it is totally out.

Also when both valves are closed (compession sroke), try to blow into the inlet/exhasut port if you can to seek a leak.

quote:

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Originally posted by smart51
What's the chance of the timing rotor slipping on the crank (or being "slipped" by a mechanic)? is is splined? My boss' suggestion was that it might have been tampered with.

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The work was done by Bruce Cribb of Cribby Tuning in Oldbury. He was recommended by the local Yamaha dealer as he used to work for them. I spoke to him on Saturday and has agreed to come to my house tomorrow to look at it. He assured me that he wouldn't leave me with the problem. I'm quite confident that he won't. I'm just trying to get it fixed, partly to make sure its nothing I've done before I get him to leave his shop for the day.

As for the engine number, it is drilled off, just as it was before, and the sealer on the rocker cover gasket was the same colour as the sealer I used last year. There seems to be less paint on the block round the exhaust ports than I remember but it seems to be the same engine.

Right-ho, the best thing you can do is to see what he says then. It's always hard to make suggestions without being stood in front of it.....

I'm sure you'll keep us posted!

The engine guy has just phoned me with one last thing to try. He suggests a squirt of oil in each cylinder, plugs back in and then try to start the engine. The oil might raise the compression enough for it to start.

Is this going to cure anything? Will starting the engine once clear something? Or is is just to prove that it is only low compression that is at fault? I guess that oil will only seal the piston rings to see if they are the cause of the low pressure.

what tappets has it? hydraulic? most likley to be shims on bikes but possibly hyrdaulic?

just wondering if the engine was upside down or on its, they could have drained or something? (although that should cause them to be open less so maybe less air is getting in so lower CR?)

do you have oil pressure?

a quick rule of thumb shows you current CR is less than 4:1; I doubt the engine would run well, if at all with it so low.

Hope you get it sorted... sorry we can't help!

ATB Steve

The tappets are bucket & shim. There is absolutely nothing that should have caused a complete lack of compression. As has already been said, he's either disturbed the cam timing (but that has been checked) or your compression tester is at fault.

I can't see you having bent valves as this would have been evident before you took the engine out, and I can't see any of your valves sticking and they wouldn't all stick (or at least one valve on every cylinder)!

One way of checking for bent valves is to check the valve clearances - if they've opened up you could have a bent valve. This is properly clutching at straws though!

[Edited on 23/10/06 by Coose]

The cam lobes push directly onto buckets with shims underneath them. The shims push the valves. I reshimmed the engine last year. I guess its possible that when the engine was upside down, the buckets could have moved and the shims slid out.

I could lift the lid again tonight and check the valve clearances.

Can't remember if I posted this before but...
Off the wall suggestion, with bike engines there is an ignition lock out if the bike is in gear with the clutch out and side stand down. Could it be during rebuild of the gear box the sensor for the neutral position has been disturbed. This can easily be incorrect if the gear box has been in and out? If you are using the origional bike loom this could be a problem. Have you got a neutral light indicator and is the engine *really* in neutral when trying to crank it over?

I spent hours by the road side when this circuit failed on my firestorm. It would spin up but not fire.

Long shot, but have you checked to see if the cam chain tensioner has been disturbed. If that was disturbed then the cam chain would almost certainly have been disturbed. But as others said, no reason for this.

Also if the timing was out significantly the values would be hitting the pistons, hence a nadgered engine.

I would get the rocker box off and see what his happening at the top end and crank it over by hand with a socket on the cranck nut.

It *could* be one of the cams has slipped its chain of the tensioner was loosened (some bike engines do this), but that could also fsk the engine. But as you say the align marks seem OK.

Long shot but if the cylinders are all reading consistently low it may even be that its always been low but coking has stopped blow by. The squirt of oil will tell you if its the piston rings that are causing low compression as the oil will temporarily seal them. Normally you get combusion carbonisation fill in some of the gap (hence haynes manuals say don't clean around the top rings if you are just doing a clean with no rebore to avoid oil consumption). If the engine was upside down/bashed about splitting cases it could be some of coking loosened and hence blow by. Even then I would expect inconsistent pressure.

As others said it may be a red herring and the compression tester may be mis reading.

Are the plugs wet (with petrol) after trying to start? If so, bad spark/timing.

[Edited on 23/10/06 by Catpuss]

A friend at work suggested removing the carbs and turning the engine over with the palm of my hand over the inlet ports. This is to guage whether one or more are leaking.

Three of them go: suck, pause, suck, pause
No2 goes suck blow, pause, suck blow, pause

I've turned the crank with a socket, with the rocker cover removed and the exhaust valve buckets move down well enough. Also, none of the valve clearances are too big, suggesting that the 3mm thick or so shims are still in place.

What could be the cause of this? I did remove all the paper towels from all the ports before fitting manifolds.

edit I took off the exhaust manifold and it works properly now. Better check the exhaust when the engine's out. So the inlet valves don't leak, which is a good sign. The engine still doesn't start even with the exhaust off.



[Edited on 23-10-2006 by smart51]

Please don't tell me there is a load of paper stuck down the exhaust blocking it up, or on the inlets

With no zorst system on you should get a bang or two, but if you are not getting that something is astray.

If Nbr 2 is OK then are zorst ports for 1,3,4 blocked? Or the inlets?

All the ports on the engine are free of the big paper towels that were stuffed in them for transport. no signs of residue or anything.

All the exhaust port towels were removed before fitting the exhaust. I can remember this clearly as I had a bit of fun removing the old exhaust gaskets. Defo no paper.

Are you sure that you've got the coils wired correctly? When I first went to start mine I had 1&4 and 2&3 swapped.....

1 to the sprocket end, 2 next to it, then 3, with 4 at the clutch end. The compression is still low, which I think to be the biggest symptom.

The bike shop guy said he's best off with the engine in his shop so they can take a look inside it. I'll carrry on stripping it out in the morning and take it up there.

I've just delivered the engine back to the shop. The guy is quite sharp eyed and noticed that 2 of the exhaust ports had shiny bits at the top of their valves. He got out a torch that was 3mm in diameter and looked into the holes and sure enough, the valves to No2 and No4 cylinders are open. This is not a good thing. They're going to take a proper look at it and get back to me.

quote:

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Originally posted by smart51
I've just delivered the engine back to the shop. The guy is quite sharp eyed and noticed that 2 of the exhaust ports had shiny bits at the top of their valves. He got out a torch that was 3mm in diameter and looked into the holes and sure enough, the valves to No2 and No4 cylinders are open. This is not a good thing. They're going to take a proper look at it and get back to me.

---

quote:

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Originally posted by smart51
I've just delivered the engine back to the shop. The guy is quite sharp eyed and noticed that 2 of the exhaust ports had shiny bits at the top of their valves. He got out a torch that was 3mm in diameter and looked into the holes and sure enough, the valves to No2 and No4 cylinders are open. This is not a good thing. They're going to take a proper look at it and get back to me.

---

The suspense is killing me too. The shop didn't get back to me yesterday and they are at a bike show today and tomorrow. More news as it happens.

If they don't tell you soon I'm gonna burst

likewise-looks like it will be monday now though

How long did this engine not run?

It could been caused by pollution on your valve's.

Are the valve's have hydraulic pushers?
Maybe the high oil-pressure opening valves due wrong oil.

This could cause open valves in some situations.

I hope there are no mechanical problems

Grtz Theo

I've spoken with the bike shop today. This is what they said:

They've soaked the bores in WD40 for a few days, then they put oil in the cylinders and did a compression test. 140 PSI in 3 cylinders but low in the other. He spoke to an engine building friend of his who said it is piston rings gummed up in the piston grooved. The best way to fix it is to refit the engine and tow it unit it starts. the heat from this will fix it.

This is beyond the limit of what I know but somehow it doesn't seem right. He asked how long it had been sat before he looked at it. It was run on Saturday and it ran just fine. On the Friday it went to the shop to be looked at. It took them 4 weeks to get it back to me plus 1 day for me to refit it. It wasn't sat around for long.

Doesn't sound quite right to me, think of it like this; if you left it stood for a month would you expect to have the same issues? no.

Alex

quote:

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Originally posted by smart51
I've spoken with the bike shop today. This is what they said:

They've soaked the bores in WD40 for a few days, then they put oil in the cylinders and did a compression test. 140 PSI in 3 cylinders but low in the other. He spoke to an engine building friend of his who said it is piston rings gummed up in the piston grooved. The best way to fix it is to refit the engine and tow it unit it starts. the heat from this will fix it.

---

christ the way this ones going you would have done better living with no 2nd gear!!!!-sounds like a fob off to me.

did they not have any further comments about the issue with the exhaust valves being open?

I asked them about the exhaust valves on the phone and twice in person. They jsut said that the valve timing is fine and that they've been through everything and it's all fine - just the piston seals. I don't feel that I know enough about engines to disbelieve them but I cant bring myself to believe it.

DID YOU get the engine where you payed for?

Looks like that you where listening to some other engine. In 4 weeks this could not happen!

It's quite feasible that the exhaust valves on 2 & 4 could be open at the same time, due to the firing order (1,3,4,2) and the valve timing. The best thing to do there is to rotate the crank to see that they do close!

The crank has to stop somewhere, and inevitably some valves will be open.....

Regarding the rings 'suddenly' being gummed up, that's just bollocks! My engine was sat for three months before I started it, and god knows how long it was sat before then!

It's quite possible that you've always had a cylinder down on compression, but just never realised. Saying that, you only just recently got it through SVA, didn't you? Hmmmm.....

quote:

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Originally posted by Coose
It's quite feasible that the exhaust valves on 2 & 4 could be open at the same time, due to the firing order (1,3,4,2) and the valve timing. The best thing to do there is to rotate the crank to see that they do close!

The crank has to stop somewhere, and inevitably some valves will be open.....

Regarding the rings 'suddenly' being gummed up, that's just bollocks! My engine was sat for three months before I started it, and god knows how long it was sat before then!

It's quite possible that you've always had a cylinder down on compression, but just never realised. Saying that, you only just recently got it through SVA, didn't you? Hmmmm.....

---

quote:

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Originally posted by smart51
I asked them about the exhaust valves on the phone and twice in person. They jsut said that the valve timing is fine and that they've been through everything and it's all fine - just the piston seals. I don't feel that I know enough about engines to disbelieve them but I cant bring myself to believe it.

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There's no such thing as a nice Pinto!

2nd gear failure is very common in bike engines due to wheelies and cack-footed gearchanges. I've just replaced the first gear in one of my bikes for this very reason!

Compression can't have been low on one cylinder until recently as the car has passed emmissions for the SVA recently - this would surely have been evident during the SVA had it of always been like that. And I'd have thought that Smart would have noticed had it lost compression before he took out the motor.

It just doesn't seem to add up. It's a shame you don't live closer as I would have offered to have a peek for you. I can't think of anyone in your area who could have a look either.....

quote:

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Originally posted by Coose
There's no such thing as a nice Pinto!

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quote:

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Originally posted by MikeRJ

quote:

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Originally posted by Coose
There's no such thing as a nice Pinto!

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Yes there is, it's just that most people couldn't justify spending the money on one.

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After lots of messing today, checking for compression and spark, I got it to start and only by squirting WD40 down the carbs. It didn't sound so good at first but by the time it got hot it was a bit better. It starts when hot no problem. We'll see how it behaves tomorrow when it is cold.

Today's trouble is that they managed to pull out the oil level sensor wire from the sensor. I tried to remove the sensor but it wouldn't budge. I've got to find a way to reconnect the wire now.

[Edited on 29-10-2006 by smart51]

quote:

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Originally posted by smart51

Today's trouble is that they managed to pull out the oil level sensor wire from the sensor. I tried to remove the sensor but it wouldn't budge. I've got to find a way to reconnect the wire now.

[Edited on 29-10-2006 by smart51]

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as the winter is coming says the weatherman get the engine up to me and ill sort it out
cheers malc

[Edited on 8/11/06 by yorkshire-engines]

If I don't get it going, I might just do that Malc.

I've taken off the head and inspected the insides. The only marks on most of the cylinders are honing marks. there are a couple of vertical marks on the "lowest" part of each cylinder at the top of the stroke but are no worse than the honing marks. The head valves don't leak solvent and the bores don't leak oil. I'm going to strip and clean the carbs next but If I can't get it to run, I'll sent it up to you.