Help diagnosing crossflow V4 failure!

[Traxion]

Looking for some input on the failure of my 95 115 crossflow V4. The #3 upper piston ring broke and subsequently destroyed the piston, head, exhaust ports, and bore (large chip). The #1 cylinder also had a broken upper ring but had not completely failed. There was nearly no carbon build up whatsoever on either piston skirt or in the ring grooves. The only other thing that was noticed was there was slight weeping around the head gasket on the block. Once disassembled, it looked as it the head gasket had been leaking on the #1 cylinder. There is discoloration/light carbon in the water jacket around cylinder #1. The separation between the block and head provided by the head gasket was also corroded through in one spot just above the #1 cylinder. The motor was hot at one time as evidenced by the coils being melted a bit. Motor has never seen saltwater, only freshwater. Cooling system since I have had it has been kept up. Lubrication system is working as far as I can tell. The other bank of cylinders were fine, no broken rings and bores were good. Bearings seemed fine throughout. Damage was limited to the pistons/bores of the #1/#3 side.

My diagnosis was that the leaking head gasket was causing combustion gasses to enter the cooling passages and along with the hole in the head gasket limited cooling to the #1/#3 cylinders. The piston crowns just got hot over time and the rings were the first piece to fail.

Any ideas beyond this? I have some photos but not on the computer yet.

 

[BonairII]

Re: Help diagnosing crossflow V4 failure!

Any chance the failed cylinders were running lean(causing it to run hot)?

Are you going to rebuild it? Or are you just curious as to why it failed?

 

[bob johnson]

Re: Help diagnosing crossflow V4 failure!

you could have had an air leak under the manifold on that side of the motor. just throwing out possibilities


is it possible the pin that prevents the rings from spinning on the piston came out??? I have heard that to be a cause of disaster.

good luck

bob

 

[Traxion]

Re: Help diagnosing crossflow V4 failure!

Thanks for the input. I plan on putting a new powerhead on the motor, the bore is damaged so badly that it isn't worth rebuilding with the parts I have got.

There is no indication of a lean condition that I can tell. Piston wash is consistent between all four cylinders, plugs read fine. The #1 cylinder is only slightly scored where the ring broke. I'll be honest I didn't pay too terribly close attention to the intake or carbs when I pulled them off but do remember them being sealed well enough. Nothing has been removed recently so unless a leak just developed I don't know where it would have come from in the near past. The ring location pins were in each piston so I know that isn't the culprit.

 

[Faztbullet]

Re: Help diagnosing crossflow V4 failure!

There is no indication of a lean condition that I can tell. Piston wash is consistent between all four cylinders

Most likely from carbon build up in ring groove due to engine running to cold... usually when one overheats enough to melt coils the t-stats are damaged and stick open and poppets melt causing engine to run cold..This results in incomplete combustion and carbon build up. Also it may have gotten hot enough to melt the deflectors which will cause it to run cold.

 

[Traxion]

Re: Help diagnosing crossflow V4 failure!

Deflectors were in good shape, all intact. The tstats were replaced when I got it and once since, so I don't think the engine was ran cold at least since I have had it. There was very, very little carbon built up in the ring grooves, but I will admit I can't say I've seen excessive carbon build up firsthand. I figured it wold be more obvious, maybe not?? Now it could have been ran cold previously and caused some damage then. But, for the last five years condition has been the same, motors has been decarbed occasionally as well.

 

[V153]

Re: Help diagnosing crossflow V4 failure!

Have you inspected the reeds?

 

[Traxion]

Re: Help diagnosing crossflow V4 failure!

Have you inspected the reeds?

Reeds were good as I could tell.

 

[emdsapmgr]

Re: Help diagnosing crossflow V4 failure!

A couple of things to check: 1. pull the carb apart that feeds the destroyed cylinder. Remove the jets (esp the high speed jet) which feeds the carb barrel to the bad cyl. Visually check for any debris in the jet, which would cause that cyl to run lean (hot.) An overheat of this type will generally not set off an overheat horn. 2. Check the damaged piston-esp the skirt area below the bottom ring. If carbon builds up around the skirt (after years of use,) and if the carbon buildup gets thick enough-it will prevent cooling gas/oil mix from getting up to both rings. Without lube and cooling (fuel), the cylinder will overheat and the top ring will crack and eventually destry the piston and head. 3. Pull the head cover off the head and check for any blockage internal to the head itself. If the head is filled with sand (or even salt, if it's a saltwater engine) both cyls can overheat internally, causing problems. 4. If the engine were overheated severely, (due to a prior bad thermostat) the engine could have suffered from an overheat "lockup." This is when the engine gets so hot that the piston expands and locks up in the cyl at high rpm's. When this failure occurs, it is possible that rings can crack and pistons can get heat-distorted-including damage to the head gasket and the intake/exhaust port area. Those port bridges are delicate. Once cooled, the engine may still run, but perhaps not like it did prior to the lockup. It is possible that any of the above overheat reasons may have damaged the seal ring on the head gasket and eventually the water leak after the initial catastrophic damage was done.