[xbird]

Been quite awhile since I checked in. I've got the Z-400 powered buggy, race at Line Mountain. Over the past years, It's been a pretty reliable choice for what I do. Original spec when i got the poor old quad that i pulled the engine from was stock carb, bassani pipe & muffler, athena 434 kit, HC # 47/48s.

About 4 seasons ago, i added an FCR 41 as stock carb was getting pretty difficult to keep dialed in, as was the valve lash. Unfortunately, I ended up dropping an intake valve. It seems the retainer may have been spreading out in the keeper area around the stem. So that lunched the head and piston, was able to save the jug. However for a season i put a stock jug and piston on it, threw in a set of used valves from a spare head and ran it that way.

In 2021, I decided to put the 434 jug back on. Had HC degree check and mark the timing points on my cams (they were bare) Added an oem spec 94mm piston and a new +4 hot rods crank (long story on how i ended up with that). I'm running the triple base gasket and triple head gasket. Loved the new found power, engine didn't seem to have any issues except for that it blew the oil pump circlip off behind the clutch. (mismatch on circlip/groove thickness) Caught that right away, so no harm, no foul I thought. Due to work and other non engine issues, I got very little seat/race time in the rig the past 2 seasons.

FFW to a couple weeks ago, fixed my chassis/suspension issues and went for a test hit. all went well. Next morning i fire it up again and it gave me some shifting issues immediately followed by the dreaded knocking ....

I retrieved a slightly mangled washer that I'm pretty sure fell off (from behind the circlip) during the oil pump incident and i didnt' realize it was floating around in there. it looks to have run up the timing chain, went through an intake cam journal and ended up back in the bottom. The knocking was a slight kiss of the intake valves on the piston. Once again, lash was fully gone to 0 on the outer intake valve. Pretty sure it jumped timing a tooth going through the chain run. Dummy me didn't check the cam positions before i pulled the head.

I have a new set of KW valves & springset on the way. have gone through the bottom end, all clean. no damage to piston or bore.

?? Has anyone ever encountered the valve lash repeatedly closing up on the intake side?

The first time it went kablammo (pre +4), I would set, run and check, and have to repeat the process to the point I was grinding shims down to spec below the HC shim kit --essentially running the bucket on the retainer and not the shim by the time i was done. Seeing the intake closed up again has me a bit worried. Cam journals/lobes have no issues.

??? Given that I added a +4, would it be worthwhile to have HC re-degree the cams?

??? Any thoughts as to this particular combo's compression and ballpark hp/torque output?
Thanks

 

[xbird]

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[xbird]

 

[bobsz]

Typically when your having intake valve issues like that, its a leaking intake system. What kind of air filtration are you running on your setup? The stock Ltz setup had issues with the filter not sealing against the air box.

 

[xbird]

Typically when your having intake valve issues like that, its a leaking intake system. What kind of air filtration are you running on your setup? The stock Ltz setup had issues with the filter not sealing against the air box.

i have a Honda 450/suzuki adapter boot carb to engine, the stock box with K&N filter lid, moose foam inside that I make sure is bolted in snug. Cut down stock rubber from the box to a custom metal elbow that goes to the carb and is overwrap sealed at that junction with a rubber boot. I used the quad's rear frame for the engine mount, but kicked the intake box up to an area that would be above the quad seat. behind my head you can see the perforated red metal (forget what it's called, for under roof eaves areas) that acts as a shield to avoid drowning the intake on big splashes, airbox is sitting on an angle behind that. The oval opening above the box to carb boot that normally got a fresh air feed boot if i recall correctly has been sealed shut.

 

[xbird]

in reading and researching more, i think the valve issues are from having been lapped in. while the valve head isn't cupped, the contact surface is showing pretty far out to the valve edge. Used sharpie and spin method just to check the old ones. i have new stainless ones, they indicate much better contact position on the valve. Also decided to replace the head. intake journal was "iffy" on this one when i got it. trying to clean up the surface wipe where the washer went thru resulted in an uneven cam, its rocking down on the journal closes to the timing gear. In viewing a bunch of heads I'm convinced they didn't put enough width on the journal on that side to prevent wear caused by the timing chain tensioner pressure. most used heads have the same journal wear on that side.