Rear Cyl compression low.

[hardhat_harry]

I'm started to look into my spare engine I have which is supposed to be smokey.

Never had it running to confirm this but I have it on the bench ready to strip down.

I have hand cranked the engine to see whether this is something obvious like crunching souned etc and it looks to be turning over fine.

One thing I have noticed is the front cylinder has loads of compression and the rear doesnt seem to have any, this is by feel as I haven't put a compression tester on it to confirm but it seems obvious.

Is this a 'character' of the SV engine or should I get the rear head open.

[fastdruid]

I bought a s/h engine for spares (for £50 :-)) with 'low' compression and it had had water ingress into one of the cylinders which had stuck the ring to the piston with rust. Probably could have 'fixed' it with just a hone and a clean, maybe new rings but as it stands its still my 'spares' engine.

Druid

[beabert]

Do you not have a compression tool handy? might aswell just rip it apart, as you are going to have to whatever the cause.

[yorkie_chris]

Check the valve clearances

[hardhat_harry]

beabert - its fairly obvious if you cover the inlet and crank the engine the front cyl has loads of pressure the back has none but I will compression test it as a final precaution when I've found the issue with the back cyl.

thanks for the input guys, off to the garage this afters to check the clearances and if not that the head is coming off.

[coxxy]

may as well bite the bullet mate, strip the whole thing down and rebuild. No point tinkering when there may well be other underlying issues as well as those known about. Be sad to get valves, bores and rings fixed up to find it has lower end problems?

[hardhat_harry]

I must admit the heads I dont have a problem with but I'm wary about pulling the bottom end apart but its sound advice.

[beabert]

I must admit the heads I dont have a problem with but I'm wary about pulling the bottom end apart but its sound advice.

Same, done everything above, but not been in a crankcase yet, a spare engine is a great way opportunity to get stuck in.

[hardhat_harry]

Well rear head and block off

Piston looks great.

Bore looks ok

mmmm Im thinking valve issue.

Another question, if I split the cases to get at the crank will the gearbox be a right pain.

[jambo]

If you're doing this to learn about the innards of an engine then fine, if you're pulling apart a block to see what's wrong with it, but not certain what you're looking for then you won't know when you've found it. Cam timing being off (but not leading to valve-piston interface) could have described everything above and required no major intervention.

None the less, enjoy the experience.

Jambo

[yorkie_chris]

Well rear head and block off

Piston looks great.

Bore looks ok

mmmm Im thinking valve issue.

Another question, if I split the cases to get at the crank will the gearbox be a right pain.

So did you check clearance before you dived in? Lot of work if you just needed to replace shim.

Also lot of work if it turns out it was just dry and needed turning over a bit to seal up again :-P

Gearbox is not hard, just put everything back same way it came out :-P

[hardhat_harry]

I was persuaded to strip it totally and rebuild but I'm debating with myself to stick the head / block back together, time it up and see what the result is.

I did have a squint into the bottom end with a torch to see if there was any sign of damage or evidence of metal fillings anywhere but its really clean.

Decisions, decisions.........

[yorkie_chris]

You won't get it now because you've opened gasket, it won't reseal.

[hardhat_harry]

Which gasket??

[beabert]

Head gasket.

I put some petrol in the combustion chamber to check if the valves are sealing correctly. Might be easier down the ports.

Also check the ring end gaps are to spec by placing them in the bore and checking with a feeler. Have you got a manual?

[yorkie_chris]

The head gasket, they're only meant to be used once

[hardhat_harry]

Is that the same for the gasket on the block too?

I also have a spare head around somewhere thats supposed to be good.

Are front and rear heads interchangeable?

[yorkie_chris]

No they don't interchange
Base gasket isn't as critical as there is no combustion pressure acting on it.

[hardhat_harry]

Yes I have a Haynes

[beabert]

Few mistakes in my haynes edition regarding timing amongst other things, so id advise you cross reference with the suzuki one floating about too.

[hardhat_harry]

Ok looks like I've found the problem. An inlet valve is not seating correctly and is leaking quite badly.

Off to a mates garage tomorrow to get the valves out and see if its just carbon build up or seat/ valve damage.

Bore is ok but I will check the ring gap while the head is away.

[beabert]

let us know :-)