no compression

[tiffy]

can anyone tell me if Triumph herald pistons are really suitable in a Jowett engine.I fitted a recon engine some while ago but no way would it start.Removed it because there was very little compression.Heads removed and as it was newly rebored assumed it was the heads at fault. Obtained a pair of recon heads,new valves guides etc.Refitted everything but same result,no compression.The best of the four readings is about 5lbs sq.in.Just stripped engine again.The cyl bore dia.is73.5mm.Thepiston dia is73mm.Top ring gap is 0.016thou.If these piston are no good where do i go now?.Thanks very much for your interest,heres hoping someone can offer good advice.

[rob needs]

There are ford fiesta pistons in mine.

[Robin Fairservice]

I have Ford Fiesta pistons in mine, and Mazda 808 pistons in my spare engine. The Fiesta's came from UK some years ago, and I understand that now they are becoming rare and expensive. The Mazda's came from the NZ club and were much cheaper. They both need some boring out of the liners.

[Drummond Black]

Tiffy, A few initial questions to gain background.

1. What other checks did you perform prior to stripping the engine ?
2. Did you check the valve lift and correctly check the engine valve timing ?
3. Did you squirt a few cc of engine oil into the bores and re-check for compression.
4. Is the crown height correct ?
5. Are you checking the compression figure with the starting handle or on the starter motor. ?

I am somewhat bewildered that with the figures you have supplied that only 5 PSI is being achieved. I ran on 1300 pistons many years ago with very good results. Even very worn pistons and bores should achieve more than 5 psi. My first theory - is enough air getting into the chamber and at the correct time. ??

Maybe the above is enough to start with and get a few comments going on your current set up. As the other lads have stated Fiesta pistons are a very good option. I have a set ready to go into a new engine being prepared for the Javelin.

Drummond

[Forumadmin]

It should be around 140 to 180 psi depending on compression ratio with normal starter motor crank speed.

It could be valve timing if the camshaft has been out.

You can check this by carefully putting a piece of soft wire through plug hole and then carefully and slowly turning handle until the wire stops coming up indicating Top Dead Centre. This should correspond to the mark on flywheel or crankshaft pulley.

If you did this on No1 piston then check that a feeler gauge (3 or 8 thousandths of an inch depending on inlet or exhaust) will go between valve stem and rocker of that cylinder. If it does not then you are either one full turn out (in which case turn crank again through 360deg) or your valve timing is completely wrong or the tappet clearance is wrong.

After this simple check then follow notes in Mike Alfrey's manual on Jowett Gallery to set up valve timing ; that is to give 12 thou lift at 12 deg before TDC (should be mark on flywheel for that).

[ian Howell]

Just a thought. What about compression height?

Do the pistons come up practically to the tops of the cylinders?

If the gudgeon pins are closer to the crown of the piston than the Javelin / Jupiter ones the result would also be lower compression.

Most likely seems to be camshaft timing though.

Keep us all informed of progress!!

[tiffy]

it seems iwas too hasty in blaming the pistons and linersy troubles.Just spent the day checking and reassembling the crankcase and reinstalling the pistons.Drummond,the two key things ididn,t do was to put oil in the bores and try again or to check the valve timing.Elementary i know but i got it fixed in my head that it must have been Triumph pistons were at fault.As you said you had used these in the past confirms what someone else told me namely that he has them in his Jupiter.Anyway at the end of the day if they are ok in triumphs they must be ok for jowetts.As for the other sugestion,the gudgeon pins are as near as i can see the same as ajowett piston.This gives me 40 thou.from the top of the piston to the liner top.All the evidence would seem to be the valve timing is/was the problem.Anyway i will put some oil in the cyl.heads combustion chambers to try and see if the valves are leaking.Thanks for your comments,will inform you of progress.

[Drummond Black]

Tiffy, I always treat a stripdown as a last resort.

Please keep us informed. GOOD LUCK

Drummond

[Drummond Black]

Tiffy, As you assemble your unit check each component carefully for wear, especially the lobes on the camshaft. If in doubt take advice.

Drummond