92 replies to this topic

[sonikk4]

You've tried 3 different heads so thats those ruled out so its got to be the liner/piston area. You have replaced the rings so if i was you find another set of pistons and try those. If the problem is still evident then it has got to be the liners.

There is no getting around it but i think that will be your next logical step, you have tried everything else.

[mk3 Cooper S]

Did you do a leakdown test?

Yes, without success. The guy whom I borrowed the gadget warned me, that soo much oil will foul the test.

But at least it approved no gasket leaks, and pressure only escaped down to the sump.

That is leaking down then !!??

[camelotr]

What brand of pistons will You recommend?

[mk3 Cooper S]

Those pistons should be fine if the bore size and liners are sound in the block.

[camelotr]

What happens if the pistons are 180 degrees urned in the bores?

[Sprocket]

Logic would normaly say to fit the pistons with the writing at the 'front' of the block, but I have not seen any pistons with a thrust side for quite some time. That was more to do with the design of the split piston skirt, which these are not.

[Sprocket]

I'll tell you what the problem is. The hone on the bore is not deep enough to remove all the boring marks, and thus, the ring seal is comprimised. two sets of different rings are not sealing in the bore, that is not a coincidence. Also, I dont recall you saying that when you fitted new rings that it was re honed?

other things to consider is the material used for the liners and the ring type, and, whether the bores are actualy round top to bottom

[camelotr]

The engine did only 1-1.5 hours befor the second ringset applied. The workshop did not rehoned the bores.

[dklawson]

If you hook up the a leak down tester (the type with two gauges) and apply 100 PSI into the cylinder and wait... then wait some more, you will get results. If the problem is the rings, all that oil will eventually be blown by the rings and back into the sump. Once that happens you'll hear an audible change in the flowing air. Give it a bit longer then take your reading off the second gauge. You will always get a little blow by even with new rings. However, I expect you'll find quickly that there is an appreciable amount of air going by (values of 75 PSI or less on the second gauge).

When you fit the rings (first or second set) did you fit them dry to the bores first (before fitting them to the pistons) to check their ring gap? Did anyone ask earlier about the actual bore and piston measurements to confirm the fit of the parts is right? If the clearance is right, the ring fit and gap are right, that only leaves the condition of the bores as Sprocket said.

[Sprocket]

The engine did only 1-1.5 hours befor the second ringset applied. The workshop did not rehoned the bores.

It should have had a hone with the new rings.

If you look in the picture you posted showing the cross hatch, you can still see the horizontal scoring from the boring operation. The hone is suposed to remove all of this leaving a 30 to 45 degree cross hatch. Once the rings have been run in the bore, new rings will need the bores re honing for them to seal efficiently.

Edited by Sprocket, 10 March 2010 - 10:46 PM.

[camelotr]

I have taken the engine out, and dismantled it. I will bring the block back to the machine shop and have the liners pressed out. We will pressure test the whole lot to see if anything is cracked/leaking. Then assemble with all new liners.

I have started my other engine today. Its a 1360 with stage 3-4 head. Its quite sporty I thing (built for my Cox GTM), and this is running without a puff of smoke. And the gas out of the breather is MUCH less then from the other engine. Something is realy bad there...

[1380gt]

hi there the only other cause is the head filling up with oil this is due to the front cam bearing oil hole incorrectly positioned it needs to be horizontal as the head needs to receive a pulsed feed not a continuous one this would force its way past the stem seals no matter how new they are
hope this helps

[camelotr]

Unfortunatly there is no excess oil under the valve cover. I have even tried to cut the head oil off completely - with no success.

[camelotr]

It looks like my problem is related to the cylinder head. But ad the valve stem-guide clearance have been checked, and the oil seals are new and correct. Soo it looks like the oil is getting down between the guide and the head casting.

[camelotr]

Finaly I have solve my problem.

It was a nasty rather mysterious honing related issue. Rehoning the block to accept a 0.1mm oversized piston solved it though. Thanks for You input. Special thanks to Pumaracing on Pistonheads for his help.