matt_gsxr
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| posted on 5/6/13 at 08:31 PM |
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Engine rebuild, no compression on cyl No 2
Just a quick sanity check.
I decided to swap my engine over as the old one had some problems.
Among other things I needed to put a base spacer in, so had to remove the pistons from the barrels.
Rebuilt it all (and even bought a new head-gasket).
Got oil pressure and started up the engine today.
Only running on 3 cylinders. Checked a few things; fuel seen, spark seen, compression 9atm, 0.2atm, 9atm, 9atm.
I assume that I messed up when I put the piston rings in on cyl 2.
Is there anything else worth checking before I tear it all apart?
I am pretty cross with myself for messing up, so be gentle.
Matt
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scimjim
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| posted on 5/6/13 at 08:35 PM |
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not got a valve stuck open?
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britishtrident
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| posted on 5/6/13 at 08:39 PM |
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Yes I would agree more like a valve problem - no valve clearance or bent or damaged or sticking valve.
A cylinder leak down test and should be able hear where the air is escaping.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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omega0684
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| posted on 5/6/13 at 08:52 PM |
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Did you reseat/ lap the valves when rebuilding the head?
Did you replace the rings? If you did, did you install them correctly? We're there any scratches in the bore? Blocked oil ring? Was the cylinder
honed or rebored and correct pistons replaced etc ?
I know these probably seem like naive questions but sometimes the obvious ones are overlooked?
ATB
I love Pinto's, even if i did get mine from P&O!
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matt_gsxr
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| posted on 5/6/13 at 09:05 PM |
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quote:
Originally posted by omega0684
Did you reseat/ lap the valves when rebuilding the head?
Did you replace the rings? If you did, did you install them correctly? We're there any scratches in the bore? Blocked oil ring? Was the cylinder
honed or rebored and correct pistons replaced etc ?
I know these probably seem like naive questions but sometimes the obvious ones are overlooked?
ATB
Slightly complicated answer.
Basically I have a few engines.
The engine that I put in was fine a couple of years ago except its water pump had failed, so I had swapped it out.
So, I didn't monkey with the head at all.
I didn't take the rings out, but on the gsxr1100 the crankcase and barrels are separate so when I put the base spacer in I did have to squeeze
the rings up to get them into the bore. I don't have a tool for the job so it is a bit of a pain.
All the rings moved freely in the pistons, cylinder wasn't bored or honed.
Happy to answer any further questions. Still annoyed with myself so it helps to share!
I don't have a leak-down tester, but can probably mock something up (surely detecting a complete lack of seal isn't going to require the
most hi-tech tools). Once I have remove the intake and exhaust I can probably check for seal of the valves using some fluid.
FWIW I have 3 heads, and only 1 decent set of barrels so if it turns out to be the head then that would be good.
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gaz_gaz
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| posted on 5/6/13 at 09:18 PM |
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Such low compression would normally point to a valve problem,
Check valve clearances first, then get the head off for a look
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britishtrident
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| posted on 5/6/13 at 09:20 PM |
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All you will probably need for the most basic leak down tester is the connector from a compression tester, a restrictor in the pipe work and a
pressure regulator.
For such a major leak you won't need the gauges.
Cylinder leak detector / tester compression leakage kit set petrol engines AT270 | eBay
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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matt_gsxr
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| posted on 5/6/13 at 09:30 PM |
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Thanks guys.
If it is just a valve then I can swap the head in a couple of hours.
That would be great news. Also will invest in leakdown tester for future use.
I will get out there tomorrow and report back. Too late now to be lugging the compressor around.
Matt
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cliftyhanger
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| posted on 6/6/13 at 06:00 AM |
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I made a leakdown tester by fitting an airline to each plug hole and listening where the air escaped. Crude but effective.
I used a u/s compression tester to supply the spark plug end...
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adithorp
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| posted on 6/6/13 at 06:26 AM |
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the only causes that are fixable without a strip down are either you've got a valve shim wrongly seated or you've put too big a one inso
check the clearances or... you've left a bung in the no2 inlet (unlikely but i've seen it).
rule those out and then the head has to come off.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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SCAR
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| posted on 6/6/13 at 07:57 AM |
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I would drop a small amount of engine oil down the spark plug hole of the low reading cylinder and re do the comp test. If the figure improves
dramatically the problem is likely to be bore related, probably rings. If little or no improvement the problem will be elsewhere, probably valve
related.
Given the pressure differences quoted I would guess at valve problem rather than a bore problem as that is a large variation.
Not too knowledgeable on bike engines so someone please chip in if this is poor advice.
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matt_gsxr
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| posted on 6/6/13 at 08:44 AM |
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quote:
Originally posted by SCAR
I would drop a small amount of engine oil down the spark plug hole of the low reading cylinder and re do the comp test. If the figure improves
dramatically the problem is likely to be bore related, probably rings. If little or no improvement the problem will be elsewhere, probably valve
related.
Sorry should have reported that I did throw some oil down the spark hole and it made ABSOLUTELY no difference.
Regarding a bung in the inlet, I'm fairly sure I took it out and only used kitchen roll anyway, so that is out.
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adithorp
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| posted on 6/6/13 at 09:11 AM |
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Fairly sure or completely sure? Kitchen roll sucked in under the valve would do it.
ps. I only mentioned it 'cos I knew a customer who balked at my price for fitting a recon' engine (that he'd sourced, meaning I just
got the bread and butter but no filling) so fitted it himself. He couldn't get it to run... cos' he'd left ALL the plastic bungs in.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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matt_gsxr
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| posted on 6/6/13 at 09:16 AM |
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Adi,
I bet you enjoyed that!
BTW 99.9% sure.
Matt
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SCAR
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| posted on 6/6/13 at 02:22 PM |
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Having done the oil in the bore bit and as originally indicated by such a large variation in pressure readings (assuming the inlet tract is clear) its
going to be a valve seating issue. You need to confirm the camshaft is ok (likely as the engine runs on 3) then check for a broken valve spring,
sticking or bent valve (compare the valve clearances). If still no luck you will need to pull the head and check the valve seats.
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matt_gsxr
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| posted on 6/6/13 at 10:34 PM |
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So, took the cam cover off. Removed the camshafts.
One of the buckets on the inlet to No. 2 was lower than the other, so looked like bent valve hypothesis might be good.
Removed head, inlet valve in question did appear to be seated but not clear (you can't do a fluid test without turning it upside down then all
the buckets and shims fall out). Anyway, I had already decided that I was just going to swap the head for a known good one.
Some pooling of fuel in the inlet manifold of number 2.
Bore on cyl 2 wasn't scratched although it was shinnier than I was expecting (but I am, as you have guessed) no expert.
So, swapped relevant bits over and installed new head.
Bolted it all down, installed cams, all done.
So, tried a quick compression test to prove how clever I was.
No 1 cylinder gave 8atm, No 2 cylinder gave 0atm. **** **** **** ****
Checked it again, same result.
I will look again tomorrow as maybe I've done something stupid (cam shaft wrong way around, 2 exhaust camshaft).
Generally I enjoy a bit of tinkering but I must say that 6 hours of farting around with engines to get back to where I started has dampened my
spirits!
Matt
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matt_gsxr
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| posted on 9/6/13 at 08:26 AM |
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Turns out a couple of the valve shims had got swapped on the inlet of No 2, so it had a valve leak from the "new" head that I tried.
Stupid really because that would have been a 40min fix, but I swapped cylinder heads (longer).
When I went back to the original head there was air getting through one of the exhaust valves also on No. 2 (how unlucky was that!). Still not sure
why, I cleaned the bucket and reshimmed smaller and it was all good. But then had to increase the size of the shim to get back to specification.
Maybe some dirt under the camshaft or between shim and valve, but I didn't see any.
Either way:
1) It works (just in time for the end of the good weather) and the replacement engine is MUCH nicer.
2) You were all correct. It was a valve thing.
3) I am a muppet and need to take more time and care.
Thanks for all the help,
Matt
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