Sprint Engine, valve contact

[Jon Tilson]

Can't speak for Matt but I knew the shame was tongue in cheek
and was rejected in the same spirit.

I cant even remember that far back in the thread for it to contribute to my analysys...lol.

Jonners

[Magenta Auto Sprint]

Thanks for the discussion chaps, there are some good ideas here.

I didn't know about holding the throttle open when doing a compression test, so thanks for that, battery was fully charged and I bought a new Sealy compression tester with screw in fitting, there is only me to do the work.

I thought the same as Jon; atmospheric pressure 14.5 Lb/sq in X 9.5 = 140 P.S.I but as has been mentioned cranking speed also helps etc.

I took the head off as nothing else made sense, at one point I checked the camshaft with another one to make sure it hadn't snapped, a daft notion I know as they are forged steel, all ok there too.

Tonight I took the camshaft and rocker assembley off, turned head upside down and sprayed WD40 over the inlet and exhaust valves, nothing drained away, so my valves are good.

so I think it must be a case of valve timing as mentioend before, so I will check this when I fit the head at the weekend. I have a D.T I (dial test indicator) so I will double check this.

I did also notice that the inlet valves on 1 + 2 are a straw colour but 3+4 are still shiny silver, so the cylinders have either never burned fuel or for not long enough. 3 + 4 just never pulled any vacum, with my hand over the card there was nothing, I used a boroscope to check for blockages befoere I removed anything, nothing found.

many thanks

Malcolm

[Carledo]

Thanks for the discussion chaps, there are some good ideas here.

I didn't know about holding the throttle open when doing a compression test, so thanks for that, battery was fully charged and I bought a new Sealy compression tester with screw in fitting, there is only me to do the work.

I thought the same as Jon; atmospheric pressure 14.5 Lb/sq in X 9.5 = 140 P.S.I but as has been mentioned cranking speed also helps etc.

I took the head off as nothing else made sense, at one point I checked the camshaft with another one to make sure it hadn't snapped, a daft notion I know as they are forged steel, all ok there too.

Tonight I took the camshaft and rocker assembly off, turned head upside down and sprayed WD40 over the inlet and exhaust valves, nothing drained away, so my valves are good.

so I think it must be a case of valve timing as mentioned before, so I will check this when I fit the head at the weekend. I have a D.T I (dial test indicator) so I will double check this.

I did also notice that the inlet valves on 1 + 2 are a straw colour but 3+4 are still shiny silver, so the cylinders have either never burned fuel or for not long enough. 3 + 4 just never pulled any vacuum, with my hand over the carb there was nothing, I used a borescope to check for blockages before I removed anything, nothing found.

I don't think the valve timing can be causing your problem, if it was out far enough to upset the air draw in one carb, it would do it for both!
Also your lower compressions are on the front 2 cylinders while the air draw fault is on the rear 2 so SOME air must be getting in there!
I say again, Check the throttle on the rear carb is actually opening! The only other possibility is a MASSIVE air leak at the rear end of the manifold. I'm not even sure that something like leaving the servo takeoff pipe off would spoil the vacuum that much that you'd have NO draw at the carb, plus the balance pipe built into the manifold would tend to share the effect around all cylinders.

Steve

many thanks

Malcolm

[Magenta Auto Sprint]

Put your note pad and calculator down, go outside and actually measure your compressions with a gauge. When they are all around 160 - 180 psi on a decent running engine come back here and i'll explain why..... in simple terms for you as i know you are getting on a bit
x x Matt

After what seems like a long time, I have resolved a few issues with my engine, firstly I found that my cam timing was out, not sure if it was when I first started this thread or if it was after I removed the head.

I know have cylinder pressures of 1) 135 PSI 2) 140 PSI, 3) 140 PSI 4) 145 PSI, I have checked all the tappet clearance and if anything they seem a bit tighter than 0.018 thou but nothing excessive.

the engine is a rebuilt and needs running in, so just wondering if my cylinder pressures should be higher?

many thanks

malcolm

[Jon Tilson]

I would suggest trying the same gauge on a known good running engine of similar compression ratio, so not your old landie
but pretty much anything else like your auto dolly should help you see what sort of figures your gauge gives.

The numbers dont sound that bad in terms of similarity. How is it running now? Does it have the sort of grunt you expect or is it down
on power? Start with getting ignition timing spot on from static and advance and then think about your carb needles.

Feel free to pop over if you need a second opinion.

Jonners