What am I doing wrong?

philh

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Righto,

Acquired '87 R80 RT 'project' quite some time ago. Ebay. Complete rolling chassis all sorted with new bearings, wiring and stainless screws everywhere. All powder-coated and looking lovely, not so keen on the cast wheels but hey maybe I can deal with them some other time. Tank and mudguards all present. Came with spare tank and boxes of bits. The engine was not fitted but had been thoroughly cleaned with the heads, barrels, pistons and valve gear all separately bagged and marked as L/R side. These items had also been thoroughly cleaned.

Straightforward then?

Not quite. Eventually make a start, order up gaskets, seals and O rings amongst other stuff. Fit new main seal and clutch. Mount engine and proceed to assemble top end. All goes well and pretty easy really. Torque it all up and (minus plugs) back off rocker arms and bring cylinder to TDC on compression stroke. Check timing marks and all correct. OT shows in the window. Set the clearance at 0.1 and 0.2mm. So, I start turning the engine and the exhaust valve begins to open and then stops! Spring is fully compressed even though valve is not fully open. Bring it back to TDC and check everything. All correct. Start again and the same thing happens. After many repetitions and checking timing etc the engine will only turn over with valve clearances at around 4mm. I know. With the correct valve clearance any attempt to turn the engine through its cycle results in full spring compression before the cycle is complete. This happens on all valves.

Some of the best brains in S London have stood in my garage perplexed. Top end has been disassembled and everything measured. All comes up to spec, pushrod length, overall valve height, spring height. The cam is correct and seems unmolested.

Any ideas as November 5th isn't too far off?
 
I know naff all about engine building .. so

dismantle the top end ... will the crank turn through its full cycle?

continue adding bits and turning over until you add something that stops it... and therein lies the problem..

(Told you that I know now't!)
 
ON the face of it (without being there and looking etc) it would maybe appear that there is a misatch of parts (rather than you doing anything wrong). This is nearly always the problem when picking up someone elses project - its never really quite what they say, and its NEVER straighforward. The fact is , even though it would appear that the parts are the ones for the bike/engine they may well not be.

I think if it was me I would start with the fundementals - as it appears you get coil bound valve springs across all valves/both sides (does the engine actually lock up?) i would be looking for part numbers and check that the barrels and heads are right for the block and within spec (any wild skimming of heads barrels?), the cam is the correct one and not some sort of wild racing version maybe, the valve springs are the right ones (they may be the right height but the wrong type), valve guides correct, valve seats correct, valves correct, etc etc.
 
Assuming you don't have a mismatch of parts causing excess rocker travel
And the valve springs are definitely getting coil bound not valve contact on piston crown,could it have had new seats fitted but not ground correctly?
Maybe the spring coils have excess pre load due to the valve not seating far enough into the head.
 
I know naff all about engine building .. so

dismantle the top end ... will the crank turn through its full cycle?

continue adding bits and turning over until you add something that stops it... and therein lies the problem..

(Told you that I know now't!)

Hi mate

Crank turns fine when valve clearance is set to ridiculous.
 
ON the face of it (without being there and looking etc) it would maybe appear that there is a misatch of parts (rather than you doing anything wrong). This is nearly always the problem when picking up someone elses project - its never really quite what they say, and its NEVER straighforward. The fact is , even though it would appear that the parts are the ones for the bike/engine they may well not be.

I think if it was me I would start with the fundementals - as it appears you get coil bound valve springs across all valves/both sides (does the engine actually lock up?) i would be looking for part numbers and check that the barrels and heads are right for the block and within spec (any wild skimming of heads barrels?), the cam is the correct one and not some sort of wild racing version maybe, the valve springs are the right ones (they may be the right height but the wrong type), valve guides correct, valve seats correct, valves correct, etc etc.

Afternoon

Yes, all the checks you mention have been done. Nothing appears amiss. Even measured cam lift and this too appears correct. Stumped.
 
Assuming you don't have a mismatch of parts causing excess rocker travel
And the valve springs are definitely getting coil bound not valve contact on piston crown,could it have had new seats fitted but not ground correctly?
Maybe the spring coils have excess pre load due to the valve not seating far enough into the head.

Ah, now then, with all other components being correct this maybe the thing. It would make sense but i have no reference to check against. Would this cause such a disparity in operating clearance? maybe if i upload a photo you could comment?
 
I did say in my post no 4 above "valve seats correct?" but you say in response all checked and all OK? and then you say you have no reference to check them against?

whatever, this would only really make sense if thay have either all been replaced and are the wrong type/machined incorrectly or maybe (extremely unlikey) if they are all starting to drop out at the same time. Thought - are the heads the right ones for the engine? and not been obtained at some point to be used ie they definatly came of the engine when it was running?
 
I did say in my post no 4 above "valve seats correct?" but you say in response all checked and all OK? and then you say you have no reference to check them against?

whatever, this would only really make sense if thay have either all been replaced and are the wrong type/machined incorrectly or maybe (extremely unlikey) if they are all starting to drop out at the same time. Thought - are the heads the right ones for the engine? and not been obtained at some point to be used ie they definatly came of the engine when it was running?

Sorry you are quite right, you did mention valve seats. This is the only area I have not confirmed as being in spec. I can upload a photo later for comment?

The engine was not running at purchase and was not even in the frame. The top end was disassembled in boxes. Wonder why. The previous owner obviously had the same issue or was part through some experiment and gave up. The difficult bit is spotting the issue.
 
Difficult to tell engineering issues from photos, but cant do any harm to have gander, you never know ! (we love photos here we do)
 
various shots with and without valves fitted
 

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Valve timing could be out, or you are simply setting clearances on the wrong stroke.
Someone might have machined the bottom of the barrels too, maybe trying to set the squish too close or some other cunning stunt1
 
Looks like the collets are fitted back to front?!!
They should be in the valve retainer and not sitting proud like that

You can see the valve springs are half compressed already!

Edit yes they are !! See attached Pic
 

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