Engine compression results

78jotadave

78jotadave

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Location
Palm Desert, California. (near Palm Springs)
I did an engine compression check on my 78 Jota (4C cams, Hi comp pistons) and these are the results
Cylinder 1 2 3
Closed throttle 115 125 90
Wide-open throttle 165 170 165 (psi, engine warmed up)

valve clearances IN .20 .20 .20 checked with
EX .25 .18 .20 engine cold

I did a search on the Forum in the hope of finding what specifications should be but could not find it, I have not done a leak-down test yet. Feedback, input suggestions are welcome.
The bike is running very well, no oil consumption, carbs might need a little fine-tuning synchronizing it just feels that way.

On another note, I just tossed the fork brace, 3rd set of fork seals in 10,000 miles and now the front end feels fantastic, I should have listened to Clem a long time ago. Thanks for any replies
 
78jotadave said:
I did an engine compression check on my 78 Jota (4C cams, Hi comp pistons) and these are the results
Cylinder 1 2 3
Closed throttle 115 125 90
Wide-open throttle 165 170 165 (psi, engine warmed up)

valve clearances IN .20 .20 .20 checked with
EX .25 .18 .20 engine cold

I did a search on the Forum in the hope of finding what specifications should be but could not find it, I have not done a leak-down test yet. Feedback, input suggestions are welcome.
The bike is running very well, no oil consumption, carbs might need a little fine-tuning synchronizing it just feels that way.

On another note, I just tossed the fork brace, 3rd set of fork seals in 10,000 miles and now the front end feels fantastic, I should have listened to Clem a long time ago. Thanks for any replies
Click to expand...
Dave, Really good comp test figures at wot 👌🏼
Get those exh clearances closer to .25 button her up and give it a floggin 😎
 
Generally accepted advice is for readings to be within 5psi of each other. Absolute values depend on accuracy of the gauge as well as compression ratio and state of the motor. Having said that, your readings are fine but as Hooksey says, get the exhaust clearances sorted pronto.
Meaningless exercise checking with closed throttle so ignore those readings.
Leakdown test provides more info, but as Paul says, why bother?
 
Fully agree with everything said before. Fix the valve gaps, only do wide open throttle testing and check again. pretty sure it will either fix the problem or at least get the values closer together. If not, it will indicate where to continue
 
thank you for your kind comments Dave, it still surprises me how many triple owners (some of very long ownership) do not know how to bolt in their front wheel and get the forks settled and paralell.
heres another comment
RIDE IT!

best wishes CLEM
ps if you have a fork brace your set up is 99% likely to be wrong
 
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I agree with you, Clem. Many don't understand how to "relax" the front-end when mounting things together. The same goes though for the Fork-Brace...: If you have a metal front fender, THIS is your fork brace already. On some bikes (like mine) though, there is not metal front-fender and a fork-brace can do lots of good things - if mounted correctly!

I had my bike at a local dealer (who's name I do not want to mention) roughly 22 years ago for some work. They returned the bike to me saying that my fork brace would make the fork stick after compression. I could not believe it. He took the bike off of the center stand, pushed the front down and - it stuck down there! :oops:

I asked him if they relaxed the whole setup. "We spent about 2 hours just on trying to get this fixed. Just bin this sucker and you are good!"

I took the bike home on the trailer. At home it took me roughly 15 minutes to mount everything correctly, relax the front end (including the fork brace) and get everyting working as it should. Fork is super sensitive, fork brace is still in place after 22 years and not one oil seal had to be exchanged.

It's all about relaxing all components when you install them from top down to the axle.
 
Laverdalothar said:
I agree with you, Clem. Many don't understand how to "relax" the front-end when mounting things together. The same goes though for the Fork-Brace...: If you have a metal front fender, THIS is your fork brace already. !
Click to expand...
If the steel front fender is mounted properly, it is mounted in rubber, which doesn’t do much in terms of acting as a brace.

Marnix
 
sorry Marnix but Lothar is humering you, I have never known you to be wrong, not ever but this time you are, stainless front guards on Marzochi 1200's are solid mounted, they are tin things, long, and the mount flexes, it should be loose when sttling the forks, but that is extreme and unnecessary , it does zero in terms of maintaining the distance between the legs which is correct, you dont want them solid here, just extra firm, if they need to move, then let them move. heres a picture.

I hope we are still friends Marnix

CLEM
 

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My SF1 with 35mm Ceris and the drum brake had a solid mounted front guard - the rubber inserts arrived with the SF2/38mm Ceris. So a Drummer would have had a solid mount guard as well.
 
Have had a Telefix fork brace fitted to the marzos on the Motodd since 1986. Forks work perfectly and never blown seals. Motodd has cover 110000 kays.
With such long forks I think they're needed
 
motoddrob said:
Have had a Telefix fork brace fitted to the marzos on the Motodd since 1986. Forks work perfectly and never blown seals. Motodd has cover 110000 kays.
With such long forks I think they're needed
Click to expand...
Hey Rob I used a Telefix many years ago removed it prior to the 1987 La Carrera Classic made the bike weave at 110mph + speeds, once removed the bike was rock solid. I put the Tarozzi fork brace on in 2008 and I liked it but in 10,000 miles and 3 sets of seals I thought removing them might be the answer, we shall see. Initial feel after removing the Tarozzi is a very compliant suspension with a nice feel, new seals and fluids always help. Following Clem's step-by-step guide for wheel and axle placement and sequence of install was spot on everything lined up and fell into place, no force or persuasion necessary(y)(y).
 
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It's very easy to introduce pressure where it's BAD with fork braces, it takes very careful fitting to introduce zero BAD and all good effects, it can be done but it isn't easy. Even tiny effects can be hard to notice on suspension movements. Same with the bolts that hold upsidedown forks to the triple trees. To tight and you cramp the fork's action.
 
piranha-bro2 said:
My SF1 with 35mm Ceris and the drum brake had a solid mounted front guard - the rubber inserts arrived with the SF2/38mm Ceris. So a Drummer would have had a solid mount guard as well.
Click to expand...
The early triples with the 38mm Cerianis also had solid mounted mudguard brackets. If they were distorted in any way, it was quite impossible to attain acceptable fork action. Those brackets are damn solid! The rubber mounts arrived somewhere around '75-'76.

The later brackets on theMarzocchi forks are quite flimsy in comparison.

piet
 
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MarnixSFC said:
Subject was a 1978 Jota. These had the rubber mounted bracket, right? 😀

Marnix
Click to expand...
Fact remains... fork braces do more harm than good if not fitted correctly/do not fit correctly.

For them to work correctly, the rest of the fork needs to be absolutely perfect as well, no use at all to fit a brace to crooked stanchions.

piet
 
Conclusion: Fork Braces can not fix forks, they can support else perfectly maintained and assembled forks if the fork brace and rest of the components are mounted right and without causing resistance.

BTW: I don't think they are hard to mount correctly. You just have to add them to the list of things that need to be relaxed when you work on the front end and only be tightened screw by screw after bumping down the front end several times when you fastened each screw one after the other and with the "bumpinig down" method. As said, it was done in 15 minutes or less... (all other components in top conditionen!)
 
78jotadave said:
I did an engine compression check on my 78 Jota (4C cams, Hi comp pistons) and these are the results
Cylinder 1 2 3
Closed throttle 115 125 90
Wide-open throttle 165 170 165 (psi, engine warmed up)

valve clearances IN .20 .20 .20 checked with
EX .25 .18 .20 engine cold

I did a search on the Forum in the hope of finding what specifications should be but could not find it, I have not done a leak-down test yet. Feedback, input suggestions are welcome.
The bike is running very well, no oil consumption, carbs might need a little fine-tuning synchronizing it just feels that way.

On another note, I just tossed the fork brace, 3rd set of fork seals in 10,000 miles and now the front end feels fantastic, I should have listened to Clem a long time ago. Thanks for any replies
Click to expand...
Checked on my 76 3CL some weeks ago and had 140 / 135 / 140 - warm engine & fully opened throttle.
Valve clearances (cold) were
EXHAUST (1) 0,26 / (2) 0,22 / (3) 0,26
INLET (1) 0,30 / (2) 0,21 / (3) 0,21
 
sfcpiet said:
The early triples with the 38mm Cerianis also had solid mounted mudguard brackets. If they were distorted in any way, it was quite impossible to attain acceptable fork action. Those brackets are damn solid! The rubber mounts arrived somewhere around '75-'76.

The later brackets on theMarzocchi forks are quite flimsy in comparison.

piet
Click to expand...
When possible, I retrofit rubber mounted mudguard stays. I don't give a damn about the finer points of fork function on paper, but I don't like broken stays.

Paul
 
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