Rebuild problems

[dmple1230]

So I have an 85 atc250r with a lot of parts from different years I recently rebuilt top end and found out I have a long rod so I bought a spacer plate and put it together after rejetting I had very low power did a compression test and got 80psi sprayed cleaner on gaskets no idle change put oil in cylinder and got 10 more psi so new rings are on the way is there something I'm doing wrong?

[dmple1230]

Any help would be greatly appreciated

[350for350]

Hopefully, you had the cylinder honed and installed new rings the last time. Did you bore the cylinder last time? If not, there may be a lot of wear in the cylinder and if that's the case, you need to bore it and go with a larger piston.

[dmple1230]

Had an 89 cylinder on and got an 85 cylinder freshly bored and honed to 68mm new rings Pistons gaskets and spacer plate I might've tweaked a ring on install though

[ATCKevin]

I've had a ring slip past the locating pin in the groove and I didn't know it. Very frustrating!

[dmple1230]

When I was slipping jug on bottom ring popped out and got a little bent but I flattened it as best I could so that's the only culprit I can come up with for the low compression I also checked it with two different testers so new rings will be in soon so I really hope that it fixes my issue

[ironchop]

When I was slipping jug on bottom ring popped out and got a little bent but I flattened it as best I could so that's the only culprit I can come up with for the low compression I also checked it with two different testers so new rings will be in soon so I really hope that it fixes my issueDo a compression test. If that ring isn't completely flat, the top corner on the bent side is what will contact the cylinder wall instead of the flat face giving you way less seal than the full width of the ring on the flat sides. You'll always have less contact patch there than elsewhere on the ring.

As cheap as a set of rings are, I would consider just getting another set.

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[dmple1230]

Also I was wondering if my spacer plate is to thick it is 3/16 when I didn't have it the piston would hit dome

[ironchop]

Also I was wondering if my spacer plate is to thick it is 3/16 when I didn't have it the piston would hit domeNo that's the size you need.

If you run the TRX piston with the long rod crank, it won't need one because I think the TRX wristpin is located higher in the piston than the ATC piston but I could be wrong


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[ironchop]

Also I was wondering if my spacer plate is to thick it is 3/16 when I didn't have it the piston would hit domeHere....read post #6...."acecarlos" is the owner of BDT Motorsports so he's knows his liquid R's and how to build them.

https://r.tapatalk.com/shareLink?url=http%3A%2F%2Fwww%2Etrx250r%2Enet%2Ff orum%2Fshowthread%2Ephp%3Ft%3D12873&share_tid=12873&share_fid=105076&share_type=t

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[dmple1230]

I ordered new rings and did a couple comp tests got 80 psi then put a little oil in cylinder and got 10 more pounds so that must be my issue

[dmple1230]

Thanks and yes I'm running a long rod with 85 piston before I tore it down I was unaware of some mods and didn't realize my old jug was an 89 jug so I bought the spacer plate so now I have an 85 jug with spacer plate and an 89 dome

[dmple1230]

I really appreciate all the input guys I've been mad as hell that I'm not out riding yet but hopefully once these rings and new base gasket come in I'll be good to go I'm using a 3 piece metal gasket on dome I've heard of drilling out rivets and making it one piece is this a good idea?

[dmple1230]

Also is there any compression difference running this set up?

[ironchop]

I really appreciate all the input guys I've been mad as hell that I'm not out riding yet but hopefully once these rings and new base gasket come in I'll be good to go I'm using a 3 piece metal gasket on dome I've heard of drilling out rivets and making it one piece is this a good idea?

Drilling out the rivets and using only one piece boosts the compression ratio. I'm not sure how much boost.

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[dmple1230]

I just ordered a copper head gasket which should boost it some I was going to reuse metal one being it didn't even have a tank of gas on rebuild but I thought better I'm getting tired of ripping it down lol

[yaegerb]

Couple suggestions. I would ditch the spacer plate and run an 87 or 88 piston. That would ensure less leaks from the base gasket. Also, I would be damn sure I ran a uccr on that motor before you fire to ensure you are running the right octane.

[dmple1230]

Uccr? Not sure what you mean

[yaegerb]

Uncorrected compression ratio. It’s a test to determine your true compression ratio and tell you what are safe levels of octane to run. You can search the procedure and calculations on the web.

[dmple1230]

Ok thanks will do

[dmple1230]

No big bore just long rod and 68mm piston and bolt on fmf exhaust boyesen cage and reeds

[dmple1230]

So I installed new rings and gaskets still getting low compression I realized my squish clearance is way to high with this spacer plate but to low without it has anyone had a similar problem and what is the best remedy to use?

[ironchop]

So I installed new rings and gaskets still getting low compression I realized my squish clearance is way to high with this spacer plate but to low without it has anyone had a similar problem and what is the best remedy to use?How low? What's the number?

Is the head shaved or has the cylinder been decked? Because this makes no sense otherwise. You said the piston hits the head with no spacer at all as I recall.

Did you measure the squish clearance with the spacer on, or is that what you're figuring since the compression is low?

You kick it a three or four times with the throttle wide open before reading the compression number? (I have to ask, no offense intended)....Is your compression guage trustworthy? (Mine once had a cracked o-ring at the fitting where it screws into the head and it gave me wonky readings)

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[ironchop]

Also I'm confused on the 89/85 cylinder part...

So you got the bike and it had a long rod and an 89 TRX jug on it? Was it running good before you rebuilt it?

Then, I'm gathering that you put a freshly bored 85 ATC jug and ATC piston on the long rod and bought a spacer plate so it doesn't hit the head because it was hitting, correct? Bent a ring, had 80psi after install, pulled apart and changed ring, and still have low compression? Was the jug bored to the piston? Or was the piston purchased after the bore? Cylinder to piston clearance?

The only way to be sure what spacer you need at this point is to measure the head and the piston protrusion from the cylinder deck at TDC.

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[Outlaw #24]

What was wrong with the 89 cylinder? My suggestion would be to put the 89 back on as it is superior to the 85 and put the 89 piston in it also. This will match the rod length the head dimensions will be back to normal and eliminates the need for the spacer. You say the piston is a 68mm what size is the 89 cylinder because the head may be cut for a smaller dimension or larger dimension depending? sounds to me like you may have to much area when the piston is all the way up to create anymore than 80 psi of compression! By the way if the spacer option is used correctly. this will provide more bottom in each gear and smoothen out the performance of the engine! Just sayin

[dmple1230]

Yes the cylinder was bored to match piston the 89 head I have would need to be rebored with the spacer plate I have 144 thousandths of squish without the plate the piston will come in contact with the dome I used two different compression testers and kicked over until the needle would not move I am now going with a thicker base gasket and deleting the spacer plate which should give me my correct clearance

[Outlaw #24]

What did you find out?