1981 G1 low compression causes

[Prof100]

I just did a compression check and barely reached 75 psi. Is that caused by a ring problem or crank seal problem or both?

[slonomo]

Could be both. A visual inspection is the only way to determine. Crank seals are very common. Usually you'll see oil around the crank seals.

[Prof100]

Originally Posted by slonomo

Could be both. A visual inspection is the only way to determine. Crank seals are very common. Usually you'll see oil around the crank seals.

Cranks seals look leaky. Bummer.

[slonomo]

Originally Posted by Prof100

Cranks seals look leaky. Bummer.

You know, you have to pretty much take the engine all apart to do both sides, might as well remove the jug and take a gander at the rings. A cylinder base gasket and head gasket aren't that expensive. It's an easy engine to disassemble, no valves or pushrods or cam to fuss with. I probably could have that engine out in 20 minutes and have the head and jug off in less than 5. It's about as easy as it gets. That's the great thing with the G1!

[Prof100]

Originally Posted by slonomo

You know, you have to pretty much take the engine all apart to do both sides, might as well remove the jug and take a gander at the rings. A cylinder base gasket and head gasket aren't that expensive. It's an easy engine to disassemble, no valves or pushrods or cam to fuss with. I probably could have that engine out in 20 minutes and have the head and jug off in less than 5. It's about as easy as it gets. That's the great thing with the G1!

Too bad you are not nearby.

Plowmans sells a piston and jug top end kit that would do the job.

[cgtech]

If you have visually confirmed "not good crank seals" and low compression, the deal is sealed. Rebuild time. Replacing the crank seals alone wont fix you up. You might get by with a "top end job", the bottom often survives ok. 75psi is way below "it's just the seals".

[Prof100]

Originally Posted by cgtech

If you have visually confirmed "not good crank seals" and low compression, the deal is sealed. Rebuild time. Replacing the crank seals alone wont fix you up. You might get by with a "top end job", the bottom often survives ok. 75psi is way below "it's just the seals".

Sadly, i think your are right.

[mikeasis]

Crank seals have no effect on compression! there i said it. Ive checked compression on G1 motor with no crank seals what so ever and it cracked 120 psi.

Id second the plowmans parts. However if the cylinder is able to be bored to first over OE size id suggest that first. I see 1st over yamaha pistons and rings on ebay all the time.

First Id disassemble the engine and inspect the crank side bearings and the lower rod bearing for slop. the side bearings do require the cases to be split.

Also are you sure its an 81? i ask because the 82 J17 engine is a low compression engine at 80-90 psi. Though 75 may be low even for it. The J17 engine will be stamped on the jug directly behind the primary clutch and the intake will be stamped j17 as well.

[Prof100]

Originally Posted by mikeasis

Crank seals have no effect on compression! there i said it. Ive checked compression on G1 motor with no crank seals what so ever and it cracked 120 psi.

Id second the plowmans parts. However if the cylinder is able to be bored to first over OE size id suggest that first. I see 1st over yamaha pistons and rings on ebay all the time.

First Id disassemble the engine and inspect the crank side bearings and the lower rod bearing for slop. the side bearings do require the cases to be split.

Also are you sure its an 81? i ask because the 82 J17 engine is a low compression engine at 80-90 psi. Though 75 may be low even for it. The J17 engine will be stamped on the jug directly behind the primary clutch and the intake will be stamped j17 as well.

Fairly sure it is an ‘81. It has the early solenoids. But who knows its history prior to me buying it in 1995
I will check the number stamped on the head.