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Discussion Starter #1 (Edited)
Need to do a top end rebuild on my ex-racebike GSXR1000 K8 which has been restored to commuter & weekend fun duty only. I suspect an exhaust valve is leaking in cylinder 1 as the compression is 2Bar lower than the others, the engine misfires/backfires at partial throttle, it idles unevenly, the exhaust is partially sucking from 1500 - 4000RPM & Cylinder 1 does not fire evenly like the others when I spray ether directly into the inlet manifold. The bike is a pig to ride at low speed as the throttle response is so jerky & uneven but it feels ok above 4000RPM with a bit more throttle.

I will inspect my current head when removed to see what the issue is - can remove the valves, test for leakage by pooling petrol in the combustion bowl, etc.. Hopefully I don't need to replace any valve seats & just need to replace 1 or mare dodgy valve (I have purchased a valve lapping kit & 'Persian Blue' marker to check the valve sealing depth & concentricity). I don’t know what thickness the current head gasket is but is likely to be thinner as was a race bike - need advice on what I should replace with for the road when using only premium gas/petrol.

Am an mech/elec engineer & accomplished home mechanic with semi-pro garage tools available ( I can get pretty much anything I need) - I have no fear about doing the actual work once I have the parts/tools available to me.

Please can experienced guys advise on the following key questions

- Head gasket size/thickness (stock bore) & where to buy? Is it safe to use a thinner gasket (95 & 98 RON widely available here)
- Can the job be done by leaving engine in the frame? (or at least leaving the rear part bolted in & pivot the top forward into the front wheel space)
- What special tools do I need if any (Have torque wrenches, digital callipers, feeler gauges, compressed air & power tools, etc.)
- What else should I check on old engine before rebuilding (cam wear, timing chain, cam chain tensioner etc.)
- What consumables do I need to replace (besides head gasket - head bolts, other gaskets, O-rings, etc.)
- What should I check on the donor head before fitment (Valve clearances, compression check/leakdown, leaking valves at seats, warping requiring, head shave, etc.)


All help & guidance appreciated fellas.


Ken
 

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Need to do a top end rebuild on my ex -racebike k& which has been restored to commuter & weekend fun duty. I suspect an exhaust valve is leaking in cylinder 1 as the compression is reduced, the engine misfires/backfires at partial throttle, it idle unevenly, the exhaust is partially sucking from 1500 - 4000RPM & cylinder 1 does not fire evenly like the other when I spray ether directly into the inlet manifold. The bike is a pig to ride at low speed as the throttle response is so jerky & uneven but it feels ok above 400RPM with a bit more throttle.

I will inspect my current head when removed to see what the issue is. Hopefully I don't need to replace any valve seats & just need to replace 1 or mare dodgy valve (I have purchased a valve lapping kit & 'Persian Blue' marker to check the valve sealing depth & concentricity). I don’t know what thick ness the current head gasket is but is likely to be thinner as was a race bike - need advice on what I should repalce with for the road when using only premium gas/petrol.

Am an mech/elec engineer & accomplished home mechanic with semi-pro garage tools available ( I can get pretty much anything I need) - I have no fear about doing the actual work once I have the parts/tools available to me.

Please can experienced guys advise on the following key questions

- Head gasket size/thickness (stock bore) & where to buy? Is it safe to use a thinner gasket (95 & 98 RON widely available here)
- Can the job be done by leaving engine in the frame? (or at least leaving the rear part bolted in & pivot the top forward into the front wheel space)
- What special tools do I need if any (Have torque wrenches, digital callipers, feeler gauges, compressed air & power tools, etc.)
- What else should I check on old engine before rebuilding (cam wear, timing chain, cam chain tensioner etc.)
- What consumables do I need to replace (besides head gasket - head bolts, other gaskets, O-rings, etc.)
- What should I check on the donor head before fitment (Valve clearances, compression check/leakdown, leaking valves at seats, warping requiring, head shave, etc.)


All help & guidance appreciated fellas.


Ken
#1) run a compression test on all four cylinders, go from there.
If there's a problem it will verify the fact.
 

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before ya dig into the engine, do a leak-down test, this will give ya a much better idea of what is happening..
 

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Discussion Starter #4 (Edited)
before ya dig into the engine, do a leak-down test, this will give ya a much better idea of what is happening..
I did a leak down test with a cold engine & could not get conclusive results on Cylinder 1 - it was in the same general range as the other cylinders basically. I couldn't hear any hissing out of the exhaust pipe of intake manifold either. The compression test showed Cylinder 1 almost 2bar lower than the others which were even - 13.5bar for Cylinder 1 vs 15.5bar for Cylinder 2,3 & 4.

What my guess is that that it's a small leak on one of the exhaust valves that is far more apparent with the engine warm than cold.

The head needs to come off & I want to do it anyway for my own sanity. I've done pretty much everything I can do without going at the head with no appreciable benefits to it's running behaviour. (Changed sparkplugs & plug coils, checked for vacuum leaks in inlet manifold, change fuel pump & checked running pressure while on the bike, changed the throttle bodies & re-synced them, resealed the exhaust gaskets, changed the engine fuelling tune dramatically, etc.)

Maybe when I stripping down the engine I can insert a bright LED in the sparkplug hole & see if I can see any light coming out past the valves when I remove the exhaust manifold.
 
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