Piston Deck Height

[TRX370R]

I am in the process of getting the R back together after all hell broke loose on the engine on the last ride out. After I got the new stroker crank in, reassembled the cases and put the cylinder on I noticed that on TDC the piston is actually sticking out of the cylinder alittle bit. It is a Pro X cylinder and when I have the head on it it doesn't contact it because the shape of the dome. I am using the big spacer plate that esr sent me. Just wondering if this is normal because I can't remember if the old setup was the same way or not. Thanks

[papatrx]

If your piston is out of the hole you definately need to check your squish to see where its at in relation to your dome on your head. With the piston out of the hole there are several factors now that come into play.

1 You do not want your squish to be less than .030

2 Your head is now going to act like an extension of the cylinder and the side clearance must be set up accordingly other wise you get a build up of gas on the outside of the piston thereby increasing the possiblity of detonation instead of up in the dome for a good burn. Anytime you increase your bore size you will now need your head re-cut for the new piston.

3 Your compression must be checked because these are some major head modifications for this type of setup.

[JTRtrx250r]

What yr piston?

[wilkin250r]

papatrx gave some good advice, but let's start with the basics first.

No, it is generally not normal for the piston to extend above the cylinder. But let's be clear on exactly what you mean. You are talking the edge of the piston, correct? It's normal for the center of the dome to be above the cylnder, but not for the edges of the piston to be above.

How much is "a little bit"? Can it be corrected with thicker base gaskets or something along those lines?

You indicated that you put the head on, and the piston did not contact the head. But did you actually measure the squish clearance?

[papatrx]

Exactly wilkin, the "piston not contacting the head" means nothing, squish can make or break and engine. Did you add the stroker crank or was it done at a shop? What size rod is in it now?

If you are going to add a "stroker crank" everything needs to be measured first, calculations made then assembled after any machining is done and measured again after.

Adding stroke to your crank will also affect your port timing, if your port timing is fairly radical, stroking it may not make it run better. Before you start adding gaskets all over just to make it fit measure your port timing with a degree wheel and keep track of every change to see what the effects are.

Most reputable engine builders I know will not sell a stroker crank to someone unless they assemble the engine or are very confident that the customer is qualified to assemble and measure correctly. This will keep you the customer from coming back complaining about an enhancement that does not work or has ruined their engine.

[wilkin250r]

Doesn't ESR use the Pro-X cylinders?

He said ESR send him the spacer plate, he using a Pro-X cylinder, stroker crank, plus his user name, I assumed it was the ESR370 kit. If that's the case, he can probably skip the port timing calculations. They are useful information, sure, but not a neccessity like they would be if he was building a stroker motor from scratch.

But still, even with a kit, and skipping the port timing, it's STILL not normal for your piston to be above your cylinder. If it's an ESR kit, I'd give them a call.

[papatrx]

I stand corrected.

When you call ESR make sure you have the specs on the crank they sent you, I am assuming you bought the new crank from them. Also measure the spacer plate thickness and let them know that, mistakes are made and sometimes the wrong parts are sent out.

I would at the very least measure the squish to make sure it's ok, I have seen mistakes made at the big shops with wrong parts matched up and sent out. I measure everything, no matter what, but I am a fanatic about my engine's going together correctly.

I have been bitten before with this so I am speaking from experience....my own stupidity.

[TRX370R]

The engine set up that was in the bike before the damage was an ESR built 370 (actually sent the motor to them and had them install the stroker crank, bore/hone, and report the cylinder for the stroker design). I had the rod break and now I am rebuilding it myself. I ordered a 370kit from ESR, with a new stroker crank. In theory it should be the same setup that was installed from ESR. I when ahead and assembled everything, started it, broke it in, rode it for about 2 hours and everything seems to be ok althought I didn't hold it in the RPMs too long as I'm still breaking it in. As far as the piston sticking up it is actually the whole piston coming out of the cylinder bore about 1/8". Although it seems to be running ok after reading the posts I think I'll give them a call and see what they think, I just hope they don't say oh we sent you the wrong crank, split the cases again and send that one back to us.

[TRX370R]

Just got off the phone with ESR and they said that it was normal for the piston to come out of the cylinder about .040 at the edge. Nice to know that I don't have to swap out the crank or piston. Thanks for all the replies

[papatrx]

Thats correct, actually many of the large stroker motors have the piston come out of the hole where the top ring is almost flush with the deck....lots of head work required.

Remember now if you get a new top end and go to a larger bore size you must give them your head also, it will need to be cut to fit the larger piston.

[beerock]

hey wilkin, i guess that space is .40, member the convo about my piston being inside like 3-4mm

[wilkin250r]

I do, and you were still running something crazy like 230psi compression or something like that. I'm STILL boggled at what kind of absurd head work have you got that gives you those kind of numbers?