siezed piston / base gasket question

WildMax

WildMax

Member
Yammie God if your still out there - Its been awhile since I was on the site - where's all the info???

Anyway, got on the vx800 the other day. Being at least 2 or 3 years since I last messed with the engine and between what I mistakingly thought my carb settings were and the Holtzman resetting itself, I seized (4 corner) clutch side piston pretty bad. Sent the jug to US Chrome and have parts coming. Tops of the pistons looked good but the one sure seized.

I have Hauck stage 2 mods on the engine. I was using a .031 base gasket and .010 head gasket. If I drop back to stock .019 base and stock .020 head will I leave any power on the table? I know raising the base gasket on the 750 engines made a difference but not sure on the 800.

I'll try to give Hauck a call tomorrow, also.
 

side note..usually a 4 corner seizure is from no warm up time before long
WOT pull,,make sure you know the diagnoses so it don't happen again.

stock pistons??
 
Sometimes that is true but not the case here - Long warm up and carefully running 1/2 throttle for the first 20 miles. Siezed at about 10 miles.
 
No. In fact this particular sled as a whole unit is far from stock. Not another like it anywhere - guaranteed. There used to be a lot of info about it on the old site but that was probably three years ago or so.

I'm sure the seize is from overheating as a result of lean out. I ride from 3000' to 7500' in the same area so I use Holtzman Attack or Vari Flow units on my sleds. They work well but you have to install the jets to the lowest elevation. The Attack compensator will adjust itself to whatever elevation you "connect" it, which should be the lowest elevation. I have over 1000 miles on this engine without a hiccup so the settings were good. However, if the sled is stored at a different elevation other than what it is set at, the compensator resets itself to that elevation. So, in my case, for some reason I installed jets for 5000' (maybe from Big Horn riding) and did not change them back to 3000' where the sled sat - probably meant to get to it but forgot about it. (I usually write the elevation settings inside the hoods).

Other evidence points to lean running condition such as no piston wash at all across all 4. Possible contributory factors could be a sticking float but the bowl was full. No sign of detonation but also no WOT. Fuel was fresh from an empty tank and carbs contitioned for off season.

Interestingly, heat discoloration on the piston pin and bearing of the seized jug suggest lack of oil. I have been using Bender direct injection on this engine but sometimes wondered if there are any advantages to it - to be on the safe side, I changed back to mix at the pump. The lower rod bearing is normal though so the discoloration could be just transfer heat.
 
I never did like Vari Flow units you ride hard on some fast trails/lakes you come stop shut off the sleds and BS or take a leak or whatever, about a 1-2 min stop max...... then you's all pull the ropes and rip off to your destination, and while you first take off all the heat from the pipes and engine has told the tempablow thats the temp is now 70-80 degress out and its leaned out the fuel flow, but the problem arises because its only 20 out and the motor is wide open again, poof.......lean burning, this may only happen for a few seconds till the tempa blow catches up but the damage has already been done, now multiply this over a whole season and you have burned exh edges on your pistons!
A tempa blow may only pick one one or 2 cylinders based on the heat of the actual cylinder, its not picky, which ever cylinder is the hottest gets it first,maybe the Holtzman Vari Flow is different dunno but allot of the guy's in our group used to run them tempa blow's and all have removed them
and just sticked with proper jetting for the temp and alt you run in..

any rate hope you get it sorted out..
 
all the heat from the pipes and engine has told the tempablow thats the temp is now 70-80 degress out and its leaned out the fuel flow
Click to expand...

What do they use for temp sensing? Is there just a bi-metallic strip somewhere under the hood? If so why couldn't a person just place it somewhere where it won't sense underhood temps? IE: in the airbox or something where it would sense incoming air temp which would change quite rapidly upon engine start after the pee break.

Just thinking outloud

Ron
 
Mad Powersports said:
What do they use for temp sensing? Is there just a bi-metallic strip somewhere under the hood? If so why couldn't a person just place it somewhere where it won't sense underhood temps? IE: in the airbox or something where it would sense incoming air temp which would change quite rapidly upon engine start after the pee break.

Just thinking outloud

Ron
Click to expand...
if i remember back then there was somthing in the air box yes that you installed, i forget the name compensater(sp?)??

i remember they were always messing with the thing and checking jetting.
 
Holtzman drawbacks are that you can't get on the throttle if you've stopped a couple of minutes - they point that out in there installation stuff quite well. Slow drive off until the underhood temps stabilize. I try to put a lot of the hardware in the airboxes. I have put carb compensators on quite a few sleds over the years and really have had no problem other than human error (as mentioned above).

For where I ride with close to 5000' elevation and 50 degree temp changes in the same day, I like them. Impractical to tune 4 carbs and you still would be setting for safe low altitude and running like crap up high.

To answer my original question of base gasket thickness (if anyone cares), Pat Hauck told me to go with .031 or .039.
 
Port Timing

WildMax said:
Pat Hauck told me to go with .031 or .039.
Click to expand...
Hi Wildmax, I remember reading your posts a couple years back when you blowed-er-up. I to have had the same conversation with Hauck and he gave me the same 0.031 or 0.039 base gasket answer. From my experiece I can tell yah that these motors like port timing. Whether you use thicker base gaskets or raise the exhaust port or a combination of both to get what you need is up to the individual tuner. I like to do a combination of both. If Hauck raises the exhaust port only by increaing gasket thickness then I would say you would leave HP on the table if you go back to the 0.20 base gasket and 0.020 head gasket. With the 0.031 gasket in place how many rotational degree's using a degree wheel is it when you start with the piston crown at the top of the exhaust port, rotate the piston down then back up to the same start position. If you don't have a degree wheel you could measure down from the cylinder top to the exhaust port with a vernier however you would need to know if the cylinders have been decked to ensure accuracy.

/Dan
 
Thanks for the input Vmax535. I believe the engine work Hauck did for me was .050 off the heads and cc'd them, pistons drilled to 0.695 holes, 2 added intake ports drilled at 0.410. I wanted the engine set up for lots of trail torque and quickness and reliability with pump gas - not intended for the drag strip. He told me to use the .031 base gasket and I thought stock head gasket. The setup (along with clutching from a lot of tests) worked excellent for what I wanted. For some reason I changed the head gasket to .010 but it still ran great for over 1000 miles. So, it would appear the engine mods brought free breathing to the machine, how much added HP I don't know.

Yesterday, Pat thought I might go with the .039 base gasket but I asked him if that wouldn't compromise the compression and what the trade off is. Pat said it might but then he thought about it and said to stay with .031 if it was working for me.

So, you're saying keeping the exhaust port open longer is good. What do you cut the heads and use for gasket?
 
cylinder mods

The piston mod and the additional intake holes really help the motor breath. For trail riding I like 0.031 base gasket, single head gasket. 0.050 seems a bit much off the head unless he has reconfigured the combustion chamber as this would reduce your squish band by 0.040 with the 0.031 base gasket and 0.050 with the the 0.031 base gasket and 0.010 head gasket. It would also get into the combustion chamber bore diameter (ccbd) which would cause detonation. It is okay to machine into it as long as the ccbd is => then the the cylinder bore diameter. I'm sure that this is okay based on the amount of miles you have put on it since the you had problems a few years back. For trail riding I like 0.065 sqish +- 0.005". Is Hauck's squish in this range?

I feel that your set-up is dead on and can be used with stock or quad pipes. Sometimes shit just happens.

/Dan
 
Thanks again Dan. Yes, Hauck reconfigured the combustion chamber - I do not know to what calcs though. Again, I told Pat what I wanted and let him figure it out.

I'll probably stick with the .031 base gasket. This gives something like 16.4 degrees increased exhaust timing. The .039 would bump that up to about 22.2 degrees.

Good to get some tech talk going again on this site.
 
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