Looking for some input guys......just bought my first Max, a 94 with 35,000 miles. First thing I did was check compression and had apx 180-185 on all four cylinders. :eusa_dance: So I proceeded to fix her up. Pics are posted in the User Mods section under My New Max. Anyway, the other day I was on the highway and noticed that she wasn't running quite right. Started breaking up at around 4000 to 4500 rpm or around 60-65 mph. So I brought it back to the guy that just rebuilt the carbs thinking that it may just need to be adjusted some more. First thing he did was check the sync on the carbs and everything was still ok. After a test ride he again checked the compression and now the front left piston was only at around 140 so he thought it might be a tight valve. Checked all the valves and all were within specs. So now we pull out the all seeing scope and run it into the spark plug hole to take a peek inside and low and behold, the left front piston looks as though it is literally melting inside the motor and scaring is already appearent on the cylinder wall. The problem is we cant seem to figure out why this has happened. :ummm: I have only put on about 400 miles sence the first compression check to the fatal compression check. Has anybody out there heard of this happening to other Max'es? I welcome your commments, suggestions and ideas.....
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gennro
Well-Known Member
Yeah a shitty carb build job can do that. Cylinder went lean and burnt a hole in the piston.
alorio1
Well-Known Member
+1 on Genro's statement, but You need to post what type of spark plug you have in it, number of plug, and jet size if you know. Maybe Sean Morley will be on later and can elaborate on more things that can cause this. Could have been an air leak @ the boot where carb wasn't properly sealed, He will add other things I'm sure, so post up info if you can.
I'm ashamed to admit that I don't know the answer to those questions :confused2: and I wont be able to get ahold of the other guy till monday now so I'll have to get back to you on this one...:tantrum:
If it's rich it could have had cylinder wash which removed the oil lubricating the wall and it doesn't take long from there. I seriously doubt you got it lean enough to burn a hole in it though.
Sean
Sean
No, there is no hole in it, it literally looks like it started melting around the edges of the piston itself.
KJShover
Proud Vmax lover
If you do the work yourself I think replacing a piston and re-ringing the others is the lesser of the two in cost.
If you replace the engine your have an engine, but if you replace the piston and do the rebuild yourself you can take some of the cash and put it in a Venture 5th gear, trans undercutting or maybe replace all 4 pistons with larger, higher compression ones. etc.
If you replace the engine your have an engine, but if you replace the piston and do the rebuild yourself you can take some of the cash and put it in a Venture 5th gear, trans undercutting or maybe replace all 4 pistons with larger, higher compression ones. etc.
I agree with Genro.
Pinging/detonation can cause rapid deterioration of the aluminium piston crown. In serious applications (ie massively turbo'd engines) I have seen complete detonatiuon of the piston!
The most likely (but not only) cause, from your description, is the carb rebuild.
http://www.google.com.au/search?q=p...ZFYekugPgoq2SAw&ved=0CCUQsAQ&biw=1259&bih=789
Pinging/detonation can cause rapid deterioration of the aluminium piston crown. In serious applications (ie massively turbo'd engines) I have seen complete detonatiuon of the piston!
The most likely (but not only) cause, from your description, is the carb rebuild.
http://www.google.com.au/search?q=p...ZFYekugPgoq2SAw&ved=0CCUQsAQ&biw=1259&bih=789
Rusty McNeil
Well-Known Member
I'm with Sean on this one...I don't know how you could possibly screw up a carb job to get lean enough to do that.....Wrong jets wrong hole maybe????
Rusty McNeil
Well-Known Member
If all you want is to repair it I think a replacement motor is going to be cheapest...
Considering that if I am reading prior post correctly that you are going to need at minimum a cylinder hone....That means you'll need to strip the block bare and remove the heads, unless it can be poor boyed from the bottom end w/o removing the heads. Can this be Done? If it can then I'm wrong and it could be cheaper......
By the time you spend money for ALL the miscellaneous items to even fix only whats broken, re-assemble the whole engine, and do all the work yourself, you're going to be close to the average $1500 for a running motor....
beware the mod monkey...my engine started out as a simple tranny repair, couldn't see not putting new bearings it it, then rings, then figuring rings and hone why not bigger, and bigger and bigger....it's like some kind of evil drug that won't let go until your wallets empty
Yeah, Im beginning to think that just replacing the motor will be the cheaper of the two options given that I can find a running one at a resonable price. Looking at a motor from an 89, any issues putting it into a 94?
I prob should have names this post "Melting Piston" instead of burnt piston. Met with my motor guy today and got a look for myself....it's definately melting. The other thing we noticed though is that on two of the spark plugs the ceramic was bone white while the other two were a nice light brown as they should have been and that the sparkplug boots were also starting to melt...........I'm guessing there's a definite heat problem somewhere.
I prob should have names this post "Melting Piston" instead of burnt piston. Met with my motor guy today and got a look for myself....it's definately melting. The other thing we noticed though is that on two of the spark plugs the ceramic was bone white while the other two were a nice light brown as they should have been and that the sparkplug boots were also starting to melt...........I'm guessing there's a definite heat problem somewhere.
Rusty McNeil
Well-Known Member
I'm sure it's a moot point now but google "pre-ignition" versus "detonation" and it will tell a pretty good story, some of it will be useless information but interesting nonetheless; there is a difference...---Pre-ignition is caused by sharp pointy objects in the chamber getting so hot that they are are source of ignition in and of themselves or together with detonation.....The pre-ignition can hammer on the piston and break the ring lands clean off..................Too hot of a plug can do this since it doesn't sink heat away, get's so freakin' hot it lights off the mixture all by itsself, so can sharp pointy edges on the top of some of those really exotic looking pistons if conditions are right
alorio1
Well-Known Member
I would look for an engine with low mileage, +1, and also there is one year model engine that went to 2 coil pick-up and supposedly addressed the 2nd gear popping out issue. I would definitely go thru the carbs again with a fine tooth comb and verify jet sizing for each spot, I have never heard of an engine getting so hot it melted the spark plug boots...After You get it running I definitely pull plugs on every tank of fuel for a while to make sure everything is right with fuel mixture.
Thanx for your previous input guys and so I decided to replace the motor and found one at a really good price. My only concern now is if there are any differences in the motor between an 89 and a 94? Are there any parts thats I should swap over that may have been upgraded on the 94 motor? Any info would be a plus, Thanks again guys!
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alorio1
Well-Known Member
Pick up coils and fly wheel .
Rand-5107
Well-Known Member
They went digital in 90. You need to talk to Sean. He has a list. I think you need a late model wiring harness, igniter box and some switches and relays.
Simplest way is to move over your 89 flywheel and 89 pickup coils. Everything else will work from the 94 just fine.
Sean
Sean
