Chrysler V/6 Diagnosis Critical


Subject: Chrysler V6 -H239 engine installed in a hire forklift.

Problem: Some 700 hours after a rebuild, and whilst on hire, the engine “developed” hard -to – start problems. The mechanic reported compression low.

The engine had been set up for LPG at the rebuild and we found the forklift on hire running on CNG. Suspecting valve recession we removed the rockers from the worst cylinder and detected a worn guide.

The mechanic was requested to shim the rockers up and to do a 2nd compression test, then call us.

We suspected problems with either one or both the distributor and the gas system to have caused abnormal exhaust temperatures.A burnt valve guide would then scrub the seat insert out to then run beyond the lifter range and hold the valve of the seat. Seen it all before; here it is again.

The following morning we are asked by the same customer to inspect the 2nd V6 we had in our shop from them if it had adjustable rockers. They had sought help from Japan overnight and were informed that a mix up may have occurred and that this was the problem !!!!! Then we were informed that the distributor was siezed, they had removed the heads, and couldn’t establish what was wrong. Oh and they had evidence of water in the cylinders.

Cause: With all this “evidence”, and I desire to make the customer happy, we proceeded to investigate the water problem by pressure testing for an insert cut into water, and to evaluate the extent of wear resulting from the siezed distributor. The mystery deepened when the guide wear was only five thou and very little seat wear existed. Abnormal for sure; but this could not be the problem.

Back to basics: all lifters were removed from the engine and fully bled down. The plan was to refit a head and using the bled lifters we would assess the accuracy of our valve installed height data.

Back to the forklift again and by now a mechanic has scraped carbon from the piston tops and behold..,……. what are all those little marks on each piston crown right where the inlet valves operate.

Cure: Back at the shop we quickly established that we had bent inlet valves dented pride and a lesson learnt not to over look the full analysis at the very start of a warranty. Most mechanics know how to take a compression test and to interpret the result; but don t assume that their analysis will always be accurate; and try to keep them following I set pattern of tests before they pull it apart.

The cause may never be found; but we are recommending an electrical rev limiter be fitted so that the night shift {they always get the blame} can t over rev the engine. The water problem is still a mystery, but the distributor has been repaired.

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